Build a 4 x AA USB Altoids Battery

Step 9 Choosing Batteries.

I did a lot of research about batteries. Which you should appreciate because it's quite boring. Sifting through PDF after PDF looking for the right energy capacity and discharge profile.

The perfect battery for this is the NiMH Energizer E2 rechargeables. They come in a convenient pack that includes 4-AA batteries and and a charger for about $20. They have 2500mAh of current capacity and they hold their voltage levels up until the screaming end. Doing away with the need for any sort of voltage management hardware. These batteries are able to power my hard drive for up to 3 hours on their own! Three times as long when the HD is plugged into a low-power USB port.

If you decide to use alkalines, or especially Lithiums, install a diode on the positive battery wire to block current from feeding back into the batteries. It'll prevent them from overheating, leaking and "venting with fire." However, if you intend to use this only to charge your iPod or PDA, then It isn't necessary.

Please note that if you do use alkalines, or especially Lithium batteries, your voltage may be dangerously high for some electronics. So the NiMH rechargables are really the best (and most economical) option.

So there you have it. The whole setup weighs about 6 ounces. A tad heavy, but if you're seriously considering building this, then you are a geek. A geek who probably needs the exercise anyway.

Comments

[gcrdcn]

Forget about using the "old" energizer batteries, they will discharge themselves in a week. Get the newer "Pre-charged" ones, Sanyo Eneloop or those called low self-discharge

[elyk0312]

Well, i have a project to look forward to now. I just bought a bluepack iPod backup battery for 10 bucks, but this definitely has more uses than simply charging an ipod. Here's an idea: use something slightly larger than an altiods can, and possible add slots for firewire as well. Btw, very nice and stylish final product.

[computo]

hmmmmm........ (thinking...) k... PROBLEM... my ipod died. . . (sob sob, charges it, i think this is why i need this.)

[maerko]

Can i charge an ipod touch with this thing? Will it charge the device, or it will only support the power to it?

[richmix]

A note, a diode implies a voltage drop of usually about 0.7V. For those who don't know the battery math here, your average alkaline AA cell is 1.5V, totaling 6V when four are put in series. NiMH AA cells, however, are about 1.2V each, totaling about 4.8V when four are used in series. While a diode is a good idea when dealing with the higher voltage of alkalines and lithiums, remember that using NiMH batteries in that circuit will substantially lower the voltage level to 4.1V. This could cause problems for some high power devices, such as external hard drives. So in short, if you use a diode, do not use NiMH batteries--or do so at your own risk.

[mason0190]

looks purty snazzy

[mason0190]

woot