Hi Pete, with LiFe & Eneloop batteries I store them fully charged in a safe place, but for lipo’s I always store them at 3.8 volts/cell (storage charge)

I dug out an old 4 cell LiPo the other day that has been in storage for around 5 years, charged it up and it worked perfectly.

The main thing with all batteries is to never leave them discharged. and as Mike said remove the batteries from the equipment.