Home-brew battery measuring station
 

With all the overinflated battery ratings floating around, it would be nice to have an impartial, third party, and repeatable test procedure performed on various cells. This pipe dream has been discussed a number of times, but never goes anywhere and just fizzles away into oblivion. Getting a company to perform this service is probably not gonna happen, so it's up to the R/C community to get the ball rolling. Unfortunately, the proper test equipment is rather expensive for most of us, so, I thought I'd come up with a home-brew solution made from fairly inexpensive parts.

Warning: No offense, but some of this will make no sense to many people, so don't feel bad. Some of the techy stuff is for electrically-minded people to contribute. :smile:

So, here is what I have come up with:

http://scriptasylum.com/forumpics/batt_tester.gif

The heart of this is a MMM ESC configured in high power brushed mode. This will be used to effectively vary the load to compensate for various pack voltages and rated capacity. In high-power brushed mode, the MMM could theoretically handle 360A of current. And the LVC can be used to prevent damage from "overzealous" testing.

The control circuit (labeled 556) is a basic timer circuit utilizing a 556 IC (dual 555's in one package) that will produce the throttle signal. Half of it will be configured in astable mode to get a 50Hz frequency. The other half of the chip is configured in monostable mode to get the 1ms to 2ms pulses to emulate a radio signal. This circuit could be (and has been) done with a single 555, but ESCs tend to be a little more finniky than servos, and this would provide better and more consistent control. The pot is a multi-turn version for fine tuning. The control circuit is powered via the MMM BEC, so it's pretty convenient.

The load (labeled 0.1 ohm) could probably be lower, but is currently sized to draw up to 74A @ 2s and 222A @ 6s (:oh:). Due to using the ESC, 2s would be the minimum value voltage-wise. To dissipate the power, many resistors would be placed in parallel, heatsinked, and fan cooled (yes, you heard right... a fan!).

Plottable measurements will be a bit tough. An eagletree with the high power module would be ideal, but the circuit above shows a voltmeter and ammeter (actually just a voltmeter across a very low value shunt) as an alternative. Obviously, using meters would be more difficult to measure pulses and true values, but it's an option.

This is something I'm seriously planning on putting together in the near future. Obviously, the MMM would be the most expensive part, as well as the batteries to test. I guess we'll just have to see. Thoughts, ideas, comments, and suggestions are welcome...

Great idea! I wonder if this could be the basis for a RC-M battery vault?

In regards to varying the current level - couldn't you just use a lower resistance or add/remove resistors as needed, and then vary the throttle input to achieve a desired current draw? Or would the MMM not like the switching losses and thus you have chosen for it to operate in a "full throttle" orientation?

It's definitely a very simple setup that can be extremely effective. I think other Eagle Tree recorder products use a shunt to monitor/record amp draw, so if they offer one with a high enough current rating maybe that would be the way to go?

A guy name access from rcu did some great testing - you might be able to get some ideas from him - http://www.rcuniverse.com/forum/m_8310589/tm.htm

Looks like he just hooked up some resistors and got some info on a screen. He did have a fan when he used four resistors. I want to see this testing go down.

A sort of battery vault is the ultimate goal. It would also be important that all tests be consistent and repeatable. And then, there is the question of credibility; will people trust test data from a possibly biased forum member?

Yeah, I suppose you could have banks of resistors to get in the ballpark of the current you want to test. I was envisioning several such banks all wired in parallel with CPU heatsinks and fans on them. I want to eliminate as much contact/wire resistance as possible, because at resistances less than 1 ohm, any little bit can make a big difference! Don't forget, I am talking about measuring 100's of amps here...

Not pictured, but I was also thinking of adding caps to the ouput. Since resistors are a resistive load (duh), the caps would smooth out the PWM pulses to provide a more consistent draw. Priobably use a spare car audio cap for that, but would be limited to ~5s because of the voltage rating.

Eagletree would be the way to go, but I was shooting for cheap and effective. The teade-off being lack of sampling/plottable measurements.

I see where you are going Brian. I do not mind sending some 2s packs made to your spec of the various cells I have laying around. As long as you either send them back, or test them to failure (would be nice to see the top end of what they can do...) I would not mind providing what I can. Some method of recording temp at the cells would be spiffy too, as some cells just seem to run hotter than others, at least in my "paltry" experience.

Thanks for the offer linc, I may take you up on that! I have to put this project together first. And actually, I was hoping for test subjects from Mike, MA, etc as well. That way, the cells are new and from a known source. I would send them back of course... providing they survive

Hopefully, there is enough feedback so I can improve the initial design before I start building it. Finding the resistors is gonna be a challenge though I think. 6s @ 200A is almost 4500w! Even if I limit the test duration, that's a LOT of heat. Maybe I'll save testing for next winter so this can also be used to heat the house. :lol:

Even if an eagletree had to be used, I would love to see REAL graphs for all the packs out there. That might quiet the maxamps debate, quiet the hobbycity actavists, and help hundreds of people make the right battery choices. If such a battery info bank was compiled, I think it would be a better online tool then the speed calculator.

lol, I just realized I made a mistake in my original diagram. IIRC, the three motor leads are tied to one end of the load, but the other end of the load is tied to the battery + lead. Oops. No biggie, the idea is the same.

Metallover: Yeah, I'm hoping it is useful. I don't want to spend the time and money on something no one will pay attention to...

LOL

I posted data a couple years ago on my maxamps packs... showing much better numbers than what was being talked about here. The reaction was that I must have something wrong with my eagletree or something because they wanted to believe the crappy numbers someone else got with their packs.

Trust me... if MA packs get good #'s then people here will take issue with it, and continue to march with their pitchforks and torches.

I have never, and still don't... make exaggerated claims about maxamps packs. When I posted data in the past, it showed they were not even the best packs I had at the time. My 20c kokam had the best #'s. I've also posted in the past that my Core 5000 pack had better #'s than a similar MA pack in the same test.

wow that'll be cool!

Hopefully any data I release will be accepted more readily as fair and unbiased. That's one of my fears; that people will think I'm biased because I am here...

+1

btw, feel free to delete my posts here, to keep the thread clean if you like... I won't flame you LMAO

How can you be biased when posting raw info? As long as it's all correct Info I can't see anyone thinking you're biased.

Being a "senior" member of this forum, people may claim the test results are skewed in favor of whatever Mike carries.

I do remember seeing your numbers. From what I can remember they were similar to the results I had with my maxamps packs.

Performance was not really my issue with the dozen or so packs I had. It was longevity. I had them puff just sitting, and had to weed out the bad cells to make good packs. Once I had done that the packs were decent, and I even sold them. Some are still running today, so my "backyard matching process" (trial by fire so to speak) apparently worked.

The packs I had, 3000, 4000, 5000 and 10000 cells, just did not have enough headroom to handle the setups I had going at the time. To be fair I was trying to push a MT on a 4s setup, and we all know that 4s in a heavy vehicle is hard on lipos. The fact that my trakpower packs outperformed the ma 5k packs and were cheaper kinda sealed the deal for me. Then there was the Jason incident, and that opened my eyes to the fact that money overcomes truth for some people...

Please post a link to your numbers GD, I would like to see them again, now that I have a better appreciation for lipos.

Ah, but "knowing" you will indicate that the previous statement is not the case.

In any case there will be people who discredit you due to the type of equipment you use, or the color of underwear you have on on Thursday. I am looking forward to seeing the results, and would like you to test some used cells just for my own interests. I just like to see what happens after hard use.

Great thinking Brian.

I am worrying about the MMM's input decoupling capacitors, you are pushing them really hard by this app.

IMO a programable(or just use a potentiometer to adjust) linear current source would be just fine for this application. just get a few power MOSFETs mounted on a HUGE fan-cooled heatsink, drive them with an Opamp connected as a current source, that's it.

You know what a stable and constant current means for a battery test platform, right?

I've offered to test batteries on a few forums before up to 500 watts. I have one cc-400 and 1 cba that is paid for already. It produces nice repeatable graphs , but no-one seemed interested enough to send me any packs.

I know you like to invent/engineer/build stuff , but my point/question is how much are you looking to spend on labor/equipment? This set-up seems available for about $1 per watt, maybe $500 total and can add multiple cc-400's at about the same $ per watt.

I figured it this way: I had already paid for the test equipment and didn't want to buy batteries. I thought perhaps users may send battery samples, but shipping twice really comes close to some of the battery packs I'd be testing. So then I'm left with simply buying the packs myself (packs I don't need)

We've talked about standards too, I can't remember which forum. I kinda like testing single cell for direct comparison , but doing "packs" seemed to be the choice of many users even though it requires 2,3,4,5,6 times the power.

Looking forward to the results here for sure. Someone send me a "test" pack, so I can pull the equipment out of the box ,lol. I don't think there will be any credibility issues with your testing/graphs/data/info Brian.

http://www.powerohm.com/catalog/GRCAT00.pdf

RH350?

That does bring up the issue of testing packs with wiring and connectors vs. bare cells with direct hookup. Those two methods will need to be clearly noted.

Linc... will have to search for the old posts. Is there still access to the old forum server?

Besides "knowing" BG here on the forum, I know him in person also. I can back him up 100% for what that's worth. :angel: Trusting his test results shouldn't be an issue.... but there's always a few, ya know? :na:

Yeah, I was thinking about the caps too, and was going to add several more (probably another 2000uF or more). Being a resistive load though won't have that constant ripple which heats them up, at least not as much as a motor's inductive load. I do still have to take the MMM's PWM switching into consideration though.

From some research on using FETs as a pass transistor for a high-A power supply, it takes a special type of FET (read: expensive) to operate well in the linear region (as opposed to switching). FETs would be easier to parallel though. So, that leaves paralleling a bunch of transistors - ugg. I'd need a "few" to say the least!

That type of device would be the ideal platform since that is what it was designed for. My idea was just based off things I have or can get fairly cheaply. If testing single cells, 1 or 2 of those would be sufficient power-wise.

I too am concerned about getting enough interest to justify the cost/bother of assembling this (although I could use it for my own uses too :smile:). What we really need is to set up a company that does this "right": manufacturers send in sample packs, pay a certain fee, and we provide them a "birth certificate" (similar to some car audio amplifiers) outlining its performance over a variety of tests that they can use in their advertising. Voila! A third party unbiased testing result!

I just sent in a quote request for the 350, but I would speculate that just the resistor is well over what I want to spend on this project.

For all the parts and components, I can see about $500 if I can find good deals. I have some stuff already. I have a watch on an eBay auction of 240 Dale 50w power resistors (3 ohm).

Thanks guys! Keep up the feedback. Maybe there is a better and cost-effective way to get us the data we all want (but few realize they want it).

Direct cell hookup would be the best test for the cell performance, but since we use these in packs in the "real world", I think the testing should be done that way too. Heck, even a very good cell can appear crappy if using poor assembly techniques and substandard wiring. Testing a pack would account for all of that. Of course, discrete cell results will be better than pack results, but testing packs would give people expected results. If they get cell tests, then take eagletree graphs of the pack, they may note the discrepancy and not trust the tests. Once credibilit is destroyed, then all that work/money is down the drain.

Awww, shucks! :oops:

How about doing "pre-made packs" since that's the way most are sold now. Not many users buy cells and make their own anymore. That way the lead and the cell construction would be in the picture so to speak. If I was to test packs , I think I'd like to limit to 2S or at most 3S and use bare leads only. That way the connector of choice would not influence the testing and it would be easier/cheaper to test them. It would still be a good enough sample to interpolate data for 3-8S packs without requiring very high power capacity.

Well, I got the reply back from the Iowa distributer (pretty quick too) and the cost is....

drumroll please.....

$749.00 (plus freight)

:oh:

Yeah, I knew it was gonna be pricey, but man! For a resistor? Granted, it is an 11,000w resistor, and nothing that beefy is gonna be cheap. Wow. Looks like I'll be making a resistor bank!

That's kinda what I was thinking anyway. I just figured the ESC was good up to 6s, so why not? At least the option for higher power will be available. Still, to get say, 200A, out of 2s, I would need 0.037 ohms. To get that, I'll need a bank of 81 resistors at 3 ohms each. I'm gonna need to build an addition to the house. :lol:

I agree; the bare leads idea is probably the best. I'll probably make a bus bar setup where I solder the bare leads to the bars for the least amount of contact resistance. No alligator leads for this thing!

before going any further i'd confirm with pdc that nothing funky in esc elecs that would stop it driving a resistor vs a motor...

an oil bath maybe easier than fans...

You could find a way to hook up an OLD space heater to act as a resistor... I have an old one that's so inefficient.. It's 1500 watts, tripped a breaker a couple times.:yes:

If anything, it would work better. No inductance, no phase angles, no "current leading voltage", etc. Purely resistive loads are always easier to drive. Which is why some devices use caps to cancel out inductance for power factor correction to make the load appear more resistive. I suppose it wouldn't hurt to ask him though, if he answers his PMs...

That would work if I was testing 120v batteries. That heater's element is around 10ohms. I would need at least 3s just to get 1A out of it. Thanks for the suggestion though!

That was my concern though - I'd bet castle uses some of that feedback to tweak operation of the motor...

I was thinking it would be possible to make a "reverse power supply" fairly easily. Convert the voltage from the battery to 110v for the space heater. The space heater may even have a power supply to step down the voltage a little?

Or, instead of a resistor, you could hook itup to a bigger motor driving a fan or something....

Can you put the power back into the grid... Be cool to get your meter going backwards....

Charger the batteries at work - discharge at home - tee hee

I really like the idea, but I do have some concerns with the setup and the dependability of the data. Namely, I don't know how you will credibly report #'s. You can watch in person and record #'s, put them in excel and make graphs. I can do that too w/o doing anything other than making stuff up. You will post it up, and there will be huge controversy of the credibility of the data. The members here will trust your results, but outside of a small sphere, it won't have merit.

I've thought about this for a while and here are some of my thoughts.
Why are you using a purely resistive load? What is the consistency of this test method and durability? How much will the resistors degrade over such harsh treatment? If the results are not very repeatable, ie resistances change slightly over temperature or time due to breakdown, your test will lack necessary sensitivity, and will not be able to make good comparisons done to tests 6mos or 30 cycles previous.
If a resistor blows and needs replacement, the test setup has fundamentally changed and would need some validation of its capability of reproducing earlier results.


Now, I had considered using a mechanical load, basically a dyno. A motor could spin up a set of weights, and the data could be recorded electronically by an ET. By using hall sensors, you can even get rpm data of the spinning weights. Add temp probes if you want too. What you can produce in the end is a graph of all these factors (rpm, amps, volts, temp, etc) on a single chart.
Aside from just peak #'s, you could read in great detail the behavior of the cell, and get create a profile (ie how quickly the cell recovers, or is able to sustain a large transitory load, ie punchiness.) This creates a dynamic test where the resistive load tests are pretty static.

The problem I foresaw in doing this is properly controlling the thr in a reliable way. Your device may take care of this, or there may be some other clever tricks. Also, the device would have to be maintained properly so mechanical friction does not greatly increase and skew results.
However, the ET can be calibrated, which is essential for getting reliable and comparative results, plus if you used a power source like a lab power supply, you could first use it to calibrate the test system and use it as a control to normalize any deviations of the test system (ie higher friction) to produce comparable results. A high quality voltmeter like a Fluke can be used to verify voltages of the test system and can be calibrated by the manufacturer with a verifying certificate.

IE. Use lab supply to provide 7.00 volts/X amps to test system. Voltmeter is attached to monitor. ET reads data. Results of calibration read of ET, resulting voltage should be within X% (say 5% at most.) recalibrate ET as necessary. (has function to do this manually.) For each batch can be done to prove accuracy of test. It can also serve as a reference standard in each batch of tests to help comparability between batches.

Also, you could then use different weights to test diff cells. A 2500 cell may need quite a diff setup than a 5000 cell to achieve a proper load. This would also be a design concern of your system.

another benefit of ETs, raw data files can be posted and independently reviewed. Data can be exported and overlaying graphs created for individ batt comparisons. A clever web programmer could prolly create a web app to o this from drop down menus linked to a result database ( a java app or whatever.) I'm sure it would fit nicely on your website if you could do it. that way its always accessible and data not buried in some thread somewhere with 50pgs of bickering over the results as most of these things on any forum always degenerate into. (We can still have that :mdr:, but at least the info would also be somewhere easily and quickly assessable to anyone.)

Thanks for the feedback guys!

The space heater thing could work, but might be difficult to get a consistent result. It would definitely provide an adequate load though! And having the electric company pay ME sounds like a superb idea.

Finnster: You bring up a lot of valid concerns and very good suggestions. However, all those are well out of my means, and even if I could afford such a thing, there would still be the credibility issue.

Ideally, the load would be infinity variable and very high power, and computer controlled. But, that requires building custom interface hardware (USB probably), firmware for that interface, and then software to set the test parameters and read the data back at a high sampling rate. This is the ONLY way to absolutely ensure perfectly consistent testing.

But if I'm gonna go that far, I might as well create a company/service that will be taken seriously by everyone, including battery manufacturers, to be used as the "standard" for test measuring. TBH, this is all beyond me at this point.

So really, this idea is useless for the masses. It would only be good for my piece of mind, and whoever (mostly here) who would trust my findings. Definitely not worth investing thousands on something that won't be taken seriously by no more than a relative handful of people. Again, the title of the thread contains the word "home-brew". :wink:

The trouble is, there is no useful data out there except for that link posted earlier of a guy who does something similar - which I haven't looked at yet. So, while we quibble about proper data, battery specs continue to be inflated (or mis-stated) tricking many new people. It's kind of a catch 22.

Hey, if the orginal idea I posted is not exact enough, that's perfectly fine, but someone has to do something. So, it sounds like between all of us, we know what should be done, but who is gonna invest their time, and most importantly, capital, to get it done the right way?

One of my LHS has been doing very nice LiPo testing. Check out the tests and equipment used: http://www.slowflyer.ch/000000972c0e...290e/index.php

For example, they have put 202 cycles on a Kokam 4800 mAh 30C with 3C charging.

I hate the recent claims of 35C and 40C battery packs, mostly hard-cased. I bet they would drop to 3 V/cell in no time and melt before they're empty or worse, if discharged at 35C or 40C constant.
The capacity numbers are heavily exaggerated as well. I've seen graphs of a "5100 mAh 35C" LiPo and it shows the same performance as a Kokam 4800 mAh 30C. The Kokam is probably more reliable after 200 cycles, too. There's this RC plane guy who's put 1000 cycles on his battery.

But hey, who buys the Kokam if the other battery has lower price, higher current rating and higher capacity rating? I agree, we need more test data in controlled (but real-world) environment.
Here, you find the Slowflyer "testing procedure", you have to translate or read in German: http://www.slowflyer.ch/downloads/pa06002v2.pdf

Regards,
Thomas

Sounds similar to what I was envisioning, albeit a little simpler. Since I can't read German (and much is lost in translation), do they also test lipos in "car mode"? Meaning, do they test the lipos with fairly low average current and then spike the current to 8X the average? This is what cars typically see. A battery that can provide a steady, but high current, may not act the same when subjected to car-style loads.

Seems like pretty valid data could be compiled just by picking a variety of similar rated packs, and running them with an eagle tree in a properly setup rc with a certain test regiment.

Do some testing with a decent pack and the vehicle to get the draw you are looking for, then setup a "course" on a road of hard acceleration and quick hard stops. Repeat for a certain number of those cycles or for a certain time limit, or till the pack hits the lvc. It would be painfully boring, and may take an esc's life, but it would provide good info such as voltage drop, heat, runtimes, and other factors. Battery effect on the other components could also be measured.

Only issue i can see is that you would have to test batts with identical specs to provide a fixed constant for the test. Some variation in driving would exist, but it would provide a type of real world testing.

Having bench equipment would e nice, as it would eliminate some variables, but would also not really recreate the same usage that we put the lipos through.

I have generally chosen my setups due to trial and error, with a temp gun, radar gun, "seat of the pants feel" and your speed calc. Battery choice was limited to what I had at hand, and I ended up with some good numbers that I rely on but i am not sure if they will translate to other packs.

Some sort of testing is vital, as just buying lipos and giving them a try is not really feasible by most, or desirable by the rest of us who can afford it. Always nice to get the right stuff the 1st time around.

I look forward to seeing your results, and i am sure that you can get battery resellers to send you packs, just stick with 2s lipo to keep it cheap.

Sry Brian, Im not trying to shoot down your idea, but just throw out some considerations. The ideas I have are to create a robust and reliable test method, within reason of course. There is a tradeoff between cost and dependability, but not necc 1:1.

If you create a lot of data, esp say showing a certain well known brand does not perform up to its peer group, the likely consequence will be objections and complaints of the unreliability, misuse or bias in the data. The more robust method you create, the less the argument can be about the trustworthiness or competence of the test method, and more about the results of the data. Ie, it can serve more people. If you are going to go to all that trouble anyway, seems like doing it well and useful to a wide range of people.

Ex: You use a simple resistive device and measure voltage under load. Brand X shows a V drop .2v below its peers.
Is the drop due to higher resistance in the load, inaccuracy of the voltmeter, charged to a diff level, or a misreading by the analyst?
Maybe none, but no way to certify, so data is suspect. Has nothing to do w/ my personal opinions of the analyst, but Brand X supporters will view the cause in deviation in the most negative ways, and lack of robustness of the test cannot resolve the dispute.


FWIW, I am a professional scientist in a heavily regulated industry, so I have some experience with the challenges of creating reliable tests and methods. Its a PITA, but I don't think you need to go so far as all that. I do have a particular critical view of these things however.

What I am proposing shouldn't cost that much, but further cuts could be made at the expense of some dependability and robustness. Minimally I would use a device like an ET to independently collect data electronically. Helps with analysis down the line too.

A independent power source along with a reliable voltmeter shows the test device is working properly before the test was run. Does not have to be a huge amt of power, just something regular and consistent. Turn it on for a light run, collect the data thru an ET, and it serves as verification run. Verification runs should look similar to ea other and be within some tolerance.

I would then just use a ESC and motor like you say, and the motor hooked up to a load. Could be as simple as a propeller, but a spinning weight driven on a pulley would imitate cars more closely. Gearing could also change the load fairly easily, and easy to set. Rather than adding weights, it may be simpler to alter gearing for diff loads for diff sized batts.

Perhaps even a computer PSU would work, as long as its output was consistant.

Set gearing (ie 2:1,) hook PSU up, run verf. run (ie set thr to 10% and let spin up weight to speed.) Hook up batt #1, run full Test Run method (say simple as 100% thr, let level off, then end.) Repeat with batt #2., etc.

A calibrated voltmeter that could read volts at leveling off manually could corroborate ET voltage readings. Ideally this would be recorded electronically, but is beyond the scope of the project.

Verf run shows the profile of the test system. Should be comparable to other runs at same gearing and same PSU. If its fine, then test results are more trustworthy. Then download all the ET data and save into database. You can export ET data to excel (or hopefully better database programs) to create graphs. Draw graphs. If you can export and be able to overlay graphs from multiple batts, all the better.

More robust verf runs can make normalizing the data over time or test sessions easier (or even possible.)

More sophisticated thr programming could make some interesting testing, such as bouncing thr from 25% to 100% over a few secs for a number of cycles to see how well the batts transition. Don't have to do this, but would be cool.

All depends on what's doable and how far you want to go.

That is the easiest, but also most unreliable and diff to compare between runs. So may variables and working parts it hard to ensure the results you were getting were due to condit of batt, or the test equipment. I've done plenty of ET runs with the cars, they are not useless, but trying to create something authoritative or reproducible for descrete comparisons over a lot of time difficult. Hard to interpret 10min long runs for people vs a quick 30 sec spin up on a test rig.

I agree. The only valid data would come from perfectly repeatable and consistent test setup.

I've thought about this for a while and don't think a dyno would be sufficient. We know that the temperature of the motor affects efficiency, and the motor temp would certainly change in a dyno, which would affect the results. I think the load would have to be something static and relatively temperature-independent. Which means we are back again to the resistor concept.

And since I was at work, I forgot to bid on those 3ohm 50w resistors (240 count) that I was watching. Ended for ~$50 + shipping. Poo. That's a whole heck of a lot cheaper than retail!!! Hopefully I'm on the ball a little better for the next one.

I suggest you look at this a bit closer, even though you don't understand every word. http://www.slowflyer.ch/downloads/pa06002v2.pdf
Whenever you see "lade", it's charging, while "entlade" ist discharging. You can figure out the rest with the units, though.
BTW, the test reports are in English, e.g. Kokam 5000 mAh 30C: http://www.slowflyer.ch/downloads/tn07008kokam5000.pdf

On page 4, you find the shematics of the equipment.

Basically, they do "static" testing every 25 cycles or so and the rest is "dynamic". You find this on page 2 of the first document and at the end of every test report.
Yes, I would say their procedure does represent "car mode", as they pull 30C peaks and average current of 8.5C or even 10C.

Best thing is, I know my batteries will last 400 cycles and loose less than 10% capacity, IF I even get to use them that much and don't abuse them.

Brian, the load resistor idea looks fine to me. In brushed mode I don't see the MMM being harmed by a static load. Though if it concerns you, you might want to think about driving a large SCR with the 556 IC and maybe another small transistor to handle the gate current.

As far as testing static load versus dynamic load- dynamic would be great, BUT the real question about battery ratings refers to static load. IE the maximum continuous current the pack can handle.