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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:

  1. 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?
  2. 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.

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  • \$\begingroup\$ They have both 3.7V, don't they? \$\endgroup\$ – neverMind9 Jul 6 '18 at 13:47
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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?

Apple doesn't share technical specs or datasheets on their devices. You are in a better place than most since you can get them cheap and easily. Unless you take one apart, or your suppliers share some data on them, noone knows. Also, beware of those cheap chinese knockoffs. Who knows what shortcuts are taken on them. Apple prices means Apple quality. 10 dollar prices mean 2 dollar quality. You are probably not getting legit 11000mAh batteries at that price point.

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.

Assuming they follow Apple specs, Apple undoubtedly takes load balancing into account. But a single cell is easier since it doesn't require that.

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  • \$\begingroup\$ The $10 pricing is for a 'used' (reclaimed) battery which will no doubt have less capacity in it. Given the cost of the other options, I would still be happy if it had half the original capacity (however I do not know how much the capacity can degrade with lithium batteries). As far as single cell/multiple cells goes, if balancing is taken into account, would there be any changes required on my side of things to use the battery compared to a single cell? \$\endgroup\$ – jonathongrigg Apr 26 '14 at 2:22
  • \$\begingroup\$ @jonathongrigg if balancing is take into account, ie internally wired and controlled by a charging ic in the battery, then no, no change. If its not, then you need to provide a smart lithium charger to do the balancing. If the battery is wired for it, I.e. has multiple charging pins, then you do the balancing. If not wired for it, you can't. \$\endgroup\$ – Passerby Apr 26 '14 at 7:37
  • \$\begingroup\$ there's 5 contacts on the battery which makes me think that it could have a contact for each of the three cells. Could you provide an example of a decent charging circuit you could use? \$\endgroup\$ – jonathongrigg Apr 26 '14 at 7:45
  • \$\begingroup\$ @jonathongrigg without knowing what those 5 contacts do, noone can provide a charging circuit. Again, apple doesn't disclose info, and since you are getting refurbs/pulls, your suppliers don't either. Welcome to black box reverse engineering problems. \$\endgroup\$ – Passerby Apr 26 '14 at 16:47
  • \$\begingroup\$ Even the iPad mini connector has 4 contacts (cyberdocllc.com/wp-content/uploads/2014/01/…) so I don't think there's any chance there. As these batteries are highly dangerous, I'd rather not try and reverse engineer anything blindly. I guess 18650s will have to do! Thanks for all your help. \$\endgroup\$ – jonathongrigg Apr 26 '14 at 23:55

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