Asklemmy

Most cordless devices have a Lithium-Ion battery in them. For Li-Ion storage you want to keep batteries around 50% charge in a cool environment. This maximizes shelf life. For example a Li-Ion battery stored at room temperature with a full charge loses about 20% capacity per year. At 40% charge (ideal) stored in a cool environment it loses about 5% capacity per year.

If you can remove a Li-Ion battery it's better for storage. Charge to 40% (3.85V measured after resting) and put in a refrigerator. This will put capacity loss under 5% per year. Don't put them in a freezer, that will damage them.

Lead-acid and NiMH batteries have a different ideal storage condition. For 12V lead-acid you want to store them at 100% charge and trickle charge overnight at 13.80V every six months. Store at room temperature. For NiMH you want to charge to full then store at room temperature until needed.

A few weeks is fine for most devices to not take special precautions. Mostly just make sure they're stored not completely dead, but not completely full either- generally 50-60% charged prolongs their life the best. Then charge before you're ready to use.

Really, modern battery chemistries are so advanced that even just charging them and tossing them in the drawer will be fine. It's not like ye olden days of ni-cad batteries that were finicky as hell and had to be charged perfectly or else they took a memory set and became useless.

The main takeaway is don't let discharge fully. Every couple of months, check charge level and if it's under 20%, charge to about 60 for more storage.

If it's just every few weeks, it should be fine as long as you don't fully discharge and keep enough charge to be useful.

Assuming we are talking about lithium, they should be stored at about half full and at human-comfortable temps. The mfg may have specific recommendations.