Originally posted by biz-engineer It depends on your approach to battery management. If the goal is to preserve the durability of your batteries, then always select the battery that is partially charged first, and recharge the batteries only when empty. If the goal is to avoid removing the grip, then, always select the grip battery first, use the body battery as a backup.
Only charging when empty was for old NiCd batteries. These new Lithium-ion you charge when you want. They will not last longer if you empty them, actually it may be damaging if you empty a Lithium-ion battery and forget to charge it for some time. It may not accept charge if lower than a safety charge. So I say; Charge the batteries every time you have been using them for more than a few images.