Assembling The USB Battery Extender

I bought a 4-cell AA battery holder and soldered it to the socket end of a USB extension cable. Wiring is simple enough. Wire the red wire to the positive terminal and the black wire to ground. The other two wires are the USB data channels which you can ignore. I ended up with this :-

Four standard 1.2V NiMH rechargeable batteries would give out 4.8V, well within limits. Even if I get the much rarer 1.25V batteries, the combined voltage would still be within limits at just 5V. In the end, I settled for GP's 1.2V NiMH rechargeable batteries. Each of them had a capacity of 1800mAh.

The picture above shows them nestled in their USB battery charger. Yes, I use it to recharge the batteries via USB!

I installed the batteries into the battery holder and took a reading off my multimeter - 5.45V! Since I wasn't too sure if the extra voltage would kill the phone, I took a reading off the cigarette adapter which I was already using to charge my phone - 5.68V! So, I guess extra 0.45V should not be a problem!

Just to be sure, I plugged my USB fan into the power pack... It spun... I plugged my brother's iPAQ using the USB charge cable... It charged! (Yes, I chose to sacrifice my brother's iPAQ instead of my phone! ;)) Finally, I decided to plug my Smartphone in...

Well... It worked! ;)

I can now use the USB battery extender to charge my phone or power up any USB gadgets like lights, fans, mobile phone charge cables, etc., etc.