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Charging an iPhone with AA batteries

I got a Tekkeon TekCharge MP1550 AA-battery-to-USB1 charger for a backpacking trip. (Know what’s really useful pretty much anywhere? An iPhone.)

AA batteries are much more versatile than common lithium-ion battery-extender packs. You can buy AA batteries nearly anywhere that sells anything, and they hold a surprising amount of power. And as long as you can keep feeding them AAs, they’ll keep going, letting you carry quite a bit of charging capacity if you’re willing to bring a lot of batteries.

There are three common types of AA batteries today:

To test them in my iPhone 4, I discharged it to 20% (when the low-battery warning dialog pops up), then charged it back up to 100% or as far as it would go until the voltage was too low to keep charging the iPhone.3 This was not perfectly isolated, since I left the radios on and occasionally used the phone lightly during the tests. The numbers are meant to be estimates.

So here’s each battery type and the number of 20-100% charges they were able to achieve in the TekCharge MP1550, plus a popular traditional-style iPhone extended battery, the generic Monoprice lithium-ion iPhone extended battery4.

Battery type20-100% charges
Energizer Ultimate Lithium, 4 AAs2.20
AccuEvolution NiMH, 4 AAs1.21
Monoprice iPhone battery, lithium-ion0.96
Energizer alkaline, 4 AAs0.70

Two options seem to make the most sense: iPhone-specific lithium-ion batteries like the Monoprice or the more popular 3GJuice, Richard Solo, or Mophie products are best for rechargeable use, especially in situations in which you can recharge them often and only need an occasional boost.

But for long trips5 away from power sources, non-rechargeable lithium AAs are by far the best — as long as you don’t mind spending money on each set and throwing them away afterward, which are admittedly two major downsides.

It’s hard to make a case for using NiMH rechargeables to charge an iPhone, especially for backpacking, where weight is important: seven lithiums weigh just under what four NiMHs weigh. So you can get about 3.6 times the iPhone-charging capacity per gram from lithiums than from NiMHs — but you can’t recharge them.

  1. The TekCharge MP1550 would not charge the iPad, regardless of battery type. ↩︎

  2. These are just like Eneloops. Please don’t email me and suggest that I try Eneloops. I know what they are. Two of my LSD NiMH cells are Eneloops, but I didn’t use them in this test because I don’t have four of them and they’ve historically performed exactly like two AccuEvolutions.

    Generally, identical battery types from different manufacturers (in this case, NiMH LSDs) perform nearly identically. ↩︎

  3. A full charge took the same amount of time — about 151 minutes — regardless of battery type, probably because it’s limited by the rate at which the iPhone draws power. ↩︎

  4. Formerly found here, but it looks like they’ve stopped selling it. Google’s cache. These ended up being a worse deal than expected because my credit card number was stolen from them. I didn’t lose any money over it, but it cost me a lot of time. ↩︎

  5. By the way, the trip starts tomorrow morning. See you in a week. ↩︎