Recharge Discharge

On another random blog hopping exercise during a quick coffee break today I found out about this battery.

What a great idea I thought, but then I began to ponder, if the technology 'develops' (in quote marks as it may 'develop' in the same way as Windows...) and is needed to produce more electricity how much urine will be needed?

I understand that changing the compounds within the 'battery' can result in different voltage, but surely there is a limit as to how big you can make the reaction for safety reasons. Ok, I realise I may be getting ahead of technology and stretching its limitations to both the unnecessary and impractical - but this is only a whimsical pondering.

In a society that still frowns upon mothers breast feeding in public, how on earth would they react to an 'emergency battery' situation. ;)