Best Battery for Underwater Camera?

[slamilton]

I have had a Vexilar Fish Scout for a few years and generally pretty happy with it but the problem is the battery. I have gone thru 2 of them to the point they wont hold a charge. I know you are not supposed to completely extinguish them but the charge meter on the Vexilar does not work so I never know when I should stop. I have a multi-meter but the battery is difficult to access so not really realistic to do that. I was considering going lithium but then I read you are not supposed to discharge them fully either. I am tired of wasting money on batteries so maybe there is a better option? Thanks.