[Neil]

Originally Posted by Margaret Pilkington

50,000mAh BACKUP BATTERY USB PORTABLE POWER BANK For IPHONE,IPAD,ANDROID DEVICES | eBay

Is something like this no good for you?...it looks very portable and doesn't cost the earth.

I don't believe that 50Ah, it looks far to small. To many of these devices lie about their capacity. It's a Chinese thing, they write on the box whatever people want to see on the box.

Also with it's stated charge rate of 5V 1000mAh it would take about 3 days to charge from flat