Agreed... that's for Lithium Ion certainly, they don't like very high or very low charge for too long.
Top 10 Lithium Ion Battery Storage & Safety Tips | DEWALT
The Power Tool Institute is encouraging you to Take Charge Of Your Battery through proper battery selection, usage, transportation, storage and disposal.
www.dewalt.com
Interestly re:long term storage
The main considerations with the batteries seems to be to avoid complete discharge and excessive load, storage temp too.
Some of the new batteries (Makita)apparently won't operate at all if you try to do too much work with them, the electronics cuts out