I'm looking to power an Arduino based project with a sufficiently large lithium battery so it can run for hopefully a week or more of constant use (ultrasonic based traffic counter). For large capacity lithium batteries, the usual advice is to use 18650s which seem to cost around $10 each for a 3400mAh Panasonic. However, I run a phone repair business and so through my connections with suppliers in China I can pick up an iPad3/4 battery for just under $10 which is around 11000mAh or an iPad mini battery for around $7 (~4000mAh). Once you get around the connector on these batteries, they seem to offer insane value in terms of mAh per dollar spent, plus it seems difficult to find batteries of that capacity in general.
My question, and it seems to be unanswered anywhere before, is how feasible would it be to use an iPad battery in place of any other lithium battery when powering an atmega328 based system? Ideally I'd also like to be able to recharge these batteries either with solar trickle charging in the device itself or a stand-alone charger. So far I believe this would involve a couple of points:
- Are the batteries protected? Are their overcharge/low voltage cutoffs implemented in circuitry inside the battery which would mean they can be safely used outside of an iPad?
- Is the fact that the iPad 3/4 battery contains multiple cells going to cause problems with load balancing during use and charging? If this is a problem, the iPad mini contains just one cell and so may be a viable alternative.
I am hoping that it is possible to use these batteries as on the surface they appear to be an excellent, untapped source of power for many embedded projects.