I have this battery,
http://www.airsoftpost.com/matrix-11...r-p-24487.html
It is overkill, but it suits my nature
I charge before every game and charge it as soon as I get home.
Because it is so big the chances of discharging it too far are extremely small, but I don't take that chance.
With these smaller batteries and upgraded guns you really need to be careful to maintain the charge level if you use them multiple times without a top up.