I store my batteries at 87% drained in the tool. Just enough battery that the tool comes on. That way I can be well into a project, with two bolts to go for the impact, or three grease zerks left, when the battery dies. I get great exercise walking back to the shop to get another battery, from another tool, that's also mostly dead. I can then put them both on the charger, while I finish with a ratchet.
Its my health plan.