I opted for a 8-cell power bank. Around 2.50 from ebay, 2x 2.1A + 1x 1A USB outputs, plus a dual led light. This thing's got a percentage screen which is rubbish, since it's all around the place, looks like it just goes down as time goes by, nothing to do with actual soc of the cells. At least it does shut down at around 3V. I also had to use a dremmel on the inside of the case, since the fit was a bit too tight and the bottome cell would not make contact properly.
I put inside 8 liberated cells that tested to an average of under 400mAh under 1A load due to high internal resistance, however they are all above 1200mAh when tested at 500mA. That said, I suspect their cumulative capacity to be around 10000mAh under real life usage. I believe these 8-cell cases are the best way to put old cells to good use, up until they get so old that they start self-discharging on their own.
Do you know of a way to measure the total capacity that's coming off of the USB port?
