Parallel batteries discussion

[BrianG]

I've read a number of threads talking about paralleling batteries (especially lipos) and have some questions - mainly curiosity. I've tried the search function, but turn up too many results to sort through.

Anyway, how do you keep parallel batteries from trying to charge the other (which in effect would discharge one while doing so)? One parallel "leg" will most certainly have slightly different parameters and will discharge faster than the other which will cause the other to try to charge the other one. The net effect of course is that the output is constant, but the charge/discharge effect could be happening "behind the scenes". I suppose a precisely matched set would be better, but they would have to be matched across the whole discharge curve.

You could use diodes to isolate them from each other, but the resulting voltage drop (.7v) times the current draw requires high power diodes - not to mention you don't get full battery power to the load. At 50 amp draw, a diode would need to dissipate 35 watts, which is power I'd rather have at the motor.

Has anyone analyzed the effects of paralleling batteries in this regard?

I would think with the relative complexity of charging/discharging lipos that this would be a greater concern.

I've never, ever, seen a real-world application where batteries are hooked in parallel - whether in R/C, UPS battery back-up systems, vehicles, etc. If larger capacity is required, you simply increase the size of the battery cells. Of course I realize this sometimes isn't feasible for R/C.

Anyway, just curious. :)