There’s also the self discharge aspect of things: cells lose energy even if you draw no current at all. This is dependent on many things including chemistry, quality, buildup, temperature and whatnot. I am not including lithium batteries (not bare cells) which need to have some kind of protection circuitry that also draws a bit of power.
It's not a chemical battery. The energy comes from the nuclear desintegration of radioactive nickel. So the charge is inmmune to most of the usual problems.
On the other hand, I don't know how strong are the layers that aborb the radiation and cretes the electricity.
