1. Room temperature, dry place
A drawer or cupboard is ideal. Heat drains batteries faster, and damp can corrode the contacts.
2. No need for the fridge
Modern batteries keep well at room temperature. A cold battery can collect condensation when it warms up.
3. Keep them apart
Leave them in the pack or a battery case. Loose cells touching each other or a coin can short out and lose their charge.
4. Don’t mix old and new
In a device that takes several batteries, replace them all at once with the same type. A weak cell drags the others down and can leak.