Canon batteries - best charging regime ?

Greetings:

Regarding late model Canon batteries (MK IV 7 5D MK2), what is the best method of charging to ensure longlife.

1. Charge regularly to ensure battery is always full ?
2. Drain battery with use to a few percent remaining, then charge ?
3. If not using for a while, keep charged or leave partly charged ?

(Obviously the above constraints cannot always be followed - my reference is to whenever possible)

Thank you & "Seasons Greetings" Iain

1. No although it doesn't hurt them like older battery technologies
2. No - this is the worst thing you can do to a Lithium Ion battery. These are not the old NiMH or older technology. You actually shorten the life of a Li Ion battery if you do that. You should ONLY ever do that if you need to recalibrate the battery charge indicator because it is inaccurate. I don't know about the current Canon batteries but Nikon batteries tell you when you should do that.
3. Yes - data shows that the maximum life for Li Ion batteries is achieved by storing them at approximately a 40% charge.

so how much should you drain the batteries before charging them? I've been doing it at 20% lately for my mkIV batts.

20% is OK. Most of these newer smart batteries have a deep depletion protection circuit that actually forces you to recharge before the battery actually needs it by cutting off power output. The worst thing you can do is to discharge the battery fully and then not recharge it for a couple of weeks or more. That destroys Li Ion batteries. But you don't want to do a "zero" recharge that often. Basically, just recharge at your first opportunity after the battery goes below 50% and you'll be fine. You don't need to overthink it but don't treat these batteries like you treated NiMH or NiCad batteries in the old days by deep depleting them. Rechargeable AA's for the most part, on the other hand, are still NiMH and the deeper you can deplete them, the better.

thanks EJ!

Thank you, Iain