After 4 years of use and abuse of my various A123 packs from a 'developers kit' I bought direct from A123, I decided to post some findings on the long(ish) term findings in these little devil cells!
First off, when I bought the developer kits (2 of them, 6 in each), I used them in a dual dewalt 850 motor/dual Novak EVX setup in a heavy 1/6 scale on road car that weighed ~15lbs. I was running a 5s2p, NON-Balanced pack, while building it, I accidentally shorted out the whole pack, blew a tab right off one of the cells. I would run this setup all of summer and fall of 2006, every other day about about 2 times, sometimes 3... run, charge up immediately after, run it again, etc. Going from 3800mah NiMH 12 cells setup, this was a real shocker as far as performance went for me, especially the flat discharge!
They sat dormant all winter for roughly 5 months still NON-balanced, never touched them nor checked the cell voltages.
I ran the 1/6 scale car for about a month in the spring? Then I had to finally go brushless, so I broke and bought an FLM maxx truck, 7XL/Quark setup and split the 5s2p pack into two 5s packs and ran a parallel harness to the controller. As you can imagine, the difference in power going from a decently fast brushed setup to a brushless one was quite apparent! I bought an Eagletree soon after this and started recording runs and found the setup was drawing consistently 150amps, and upwards of 180 amps under hard thottle... soon found out that the 7XL COULD have been a 6XL mislabeled, because I was getting much too high top speed for the Kv of a 7XL. At the pack level, they got pretty warm to touch, my guess would be 135F on a 30 'C day. Ran this setup for about 2 months, and got sick of the high temps on the Feieiyadodurkadurkago 7XL, so I bought a 1512/3D (1700kv).
Now I bought some more A123 cells from DeWalt 36V batts on eBay for a 7s2p and 7s1p pack setup. I bought a Traxxas Villain EX and used the two 5s1p packs in the boat. Packs are still NON-balanced charged, but I checked the cells voltages of each pack and all seemed well, all within 0.02volts.
Since 2007 I have ran the boat all summer every few days in a large slew/pond on our property. Runtimes were about 7 mins, so about 8.5 C discharge rates. If anyone has a Villain boat, they will know that the packs are enclosed in a tight space with zero airflow, in fact, they are getting hot air being blown on them by the motors, which get pretty toasty themselves. Pack temps were consistently running around 145 - 150F right after the run, and they did increase a few degrees after a few minutes sitting. These packs are still being used in the Villain boat with no end in sight.
Packs cycles are UNKOWN, but I would put a conservative guess of 400-450 cycles.
So today I decided to put some balance plugs on the packs and give them a few cycles on the 720i. Here is what it is reporting:
-Capacity: 2065mah
Original: ~2300mah
-Cell resistance: ~32mOhm/5 = ~6.4mOhm/cell
Original: ~rated 40mOhm/5 = 8mOhm/cell
-Cell balance: all within 0.01V/cell!! End of charge more around 0.04Volts/cell
So the cells after 4 years being through several different setups and used to their limits, never balanced charged, sitting dormant 4 winters for 5 months at a time, and being charged at 3.75v/cell for the last two years, AND being shorted out before the first time they were even used... still retain 90% of their original capacity, and if the 720i is to be believed, they have LOWER cell resistance! I do remember reading in the developer kit instructions that the chemistry really does DECREASE in resistance rather than increase like a traditional LiPo (although the new gen cells are more like A123's in this respect).
I would have to say I am thoroughly impressed by what these things are able to handle. The pack resistance is the thing that gets me though, going from 8mOhm to 6.5mOhm?!? I don't really know what to make of that, I am thinking that the 720i is inaccurate in calculating this? If these packs had been balanced charged and had a little TLC over their life who knows what they are able to do.
I know what battery I am using in my ebike project! (Although their new 10Ah cell
)