Hey Joe! I was talking to Fran, and if I just keep the resistance to like 1 Ohm, then the max current draw would be 4 amps at 100% duty, so I could just keep the duty to 50%. I just didn't know that there were such precision fuses out there. I'm going to use some that last "forever" at 2amp, and last for like 10 seconds at 4 amps. Isn't that amazing that they can do that?
http://www.belfuse.com/Data/Datasheets/C1S.pdf
That way, a micro that fails full on, or a mosfet that fails shorted would be harmless.
Actually there are 2 mosfets. But I just thought of a way to check if the 2nd failed shorted too. The 2nd failure wouldn't run the battery down, it would just turn on the power to the attiny voltage monitoring circuit, which uses like 2mA. That would mean that the attiny was sending voltages. So, when the power is first applied, I could expect a particular startup sequence to be sent to the big micro from the attiny, and if it doesn't happen (if it only sends actual voltages of the battery), then you know there's a problem, like it has been running since the last time it was turned off. 2mA can be drawn from a 100amp*hr battery for a really really long time before it's a problem. If the correct sequence isn't obtained, the main charger and controller would know which naughty cell monitor was the culprit. ya!