There are plenty of threads here regarding the care & maintenance of LiPo batteries. As for dean connectors, you can purchase them at R/C hobby shops, and swapping out Tamiya contacts for deans is simple if you're handy with a soldering iron.
If you decide to use LiPo's, consider installing a MOSFET - it'll save wear/tear on your trigger contacts.
Alternatively, if you decide to stick with NiMH/NiCad, just carry a second battery pack into the field in the event your battery runs out. And since you stated that you don't require a high RoF, a high mAh rating shouldn't be a bullet point in your decision making.
VFC SCAR-L - VFC SCAR SSR - KJW Hi-Capa 5.1 - CAW M79
The Three Sisters - WE G39 E/K/C
Originally Posted by kalnaren
Stalker stays where he is.
His BB's fly across the country to hit their target.