Calculator collection : How to power calcs without constantly opening?

[EugeneNine]

I've had more Rayovac's leak than any other AA, then Energizer and then Duracell. Manufacturing lines change from time to time so the battery you buy today isn't the same as the one you bought a decade ago.
But what I've done is invested in Eneloops and schedule a annual/bi-annual swap and charge. Rechargeable NiMH are less prone to leaking (but still possible) and Eneloops have remained the highest rated since their introduction and seem to be the safest bet still.

For other voltages though the idea of a small Lithium Ion pack coupled with wireless charger would make a decent alternative. Most of the problems with lithium ion are due to device manufactures pushing them to 110% of their design to make the device charge as fast as possible and run as long as possible between charges (and wear the battery out as fast as possible in order to sell a new one, so if you charge them slower and set the charge to stop at less than 100% with a small charging ic that allows for specifying charge parameters you can make them very reliable.

Another option is to 3dprint replacement battery doors so you put the original away somewhere and use the 3dprinted clone. Make your clone door fit a little more loose so it doesn't wear out latches and such.