Rechargeable batteries have a max number of cycles that should be charged. So keeping them equally cycled there is a technique. So a method of doing this is keep them in first in to first out stack.
After recharging them put the battery in the top of the stack. Pull the out the bottom cell to be used next. No reason to count recharge cycles.
The series of pictures show the stack in a different way. Heads is the round peg, tails is the square block.
Take the next battery to be used next to the head, and move the head peg counter-clockwise to the next cell. When a freshly charge battery is ready, place it next to the tail and move the tail counter clockwise.
My son wanted a first in first out stack. So I came up with this last night. I used scrap wood for a prototype.
Shapes and sizes are up to the artist or customer.
Me. Mark Eason