I'm a LiPo guy and charge the batteries outside of the vehicles in a charging bag. Since both my vehicles that use the small packs (1300 and 1800mah used for airsoft guns) have the batteries on the outside of the vehicle disguised as equipment, I don't have the chore of having to crack the vehicles open to get to the batteries etc. I only have one tank that still uses a NIMH pack and I also charge it outside of tank. I plan on converting it over to use a small LiPo as well at some point as it will give me more room in the tank plus eliminate alot of the weight that comes with the NIMH. My Renault FT project will use a small LiPo as well when I get it finished and I'm using magnets to hold the top deck on so it hopefully won't be too much trouble in removing the battery for charging.
I'm more into light tanks or smaller vehicles so LiPo's really work best for me where size and weight are a factor. Unless I change over to LiFe batteries like Jeff's doing (and very successfully I might add, I've seen his setups), I'll just continue using them and definitly charge them outside of the vehicles.