I have been using Energizer rechargeables for my Garmin 78sc for the reason of not wanting to dispose batteries too frequently, and have not encountered capacity problems. Luck of the draw I suppose.
Just forcefully pushed the Energizer rechargeables into the dry cell battery pack and managed to fit them in. However, they expanded the inside frame of the battery pack by a little and the battery pack could no longer fit into the VHF. I ended up needing to use a screwdriver to get the rechargeables out.
I then tried to forcefully push the new Duracells into the dry cell battery pack and it could fit into the VHF, although that almost broke the two plastic legs on the top of the battery pack.
Went to Walmart last night and found a slimmer and shorter AA battery: Panasonic!!!