Need a Battery with long shelf life and high density ?
(say 50 years of standby )
Apart from Nickle Iron ... And this would be much simpler and actually doesn't need to be held at charge.
Australian company markets long-life power supply, activated by water
“The result is 30 times more power than a traditional AA battery, and best of all, is fully recyclable, free of toxic corrosive materials, is non-hazardous unlike kerosene, and will dramatically reduce disposable battery waste in landfills.”
Australian firm brings chemical free energy storage device to market – seeking to provide long term backup storage that only requires the addition of water.
Well it looks pretty :)