My crystal ball is a bit cloudy... How about a schematic and part numbers? Most 78xxx regulators will need a heatsink to reach max current output. If not their internal protection will shut them down before getting there.
So I have build the circuit, Decided to stay with the LM2940C regulator.
I have 12V out but for some reason there is no current flow to charge the battery, have tried other loads including light bulb etc and that works fine.
Thought the battery might have been too heavy a load for regulator (1 amp limit) so tried creating some parallel branches to decrease load but that didn't work either.
I have had issues with this battery only being able to charge on certain chargers, some electrical characteristic of the charger maybe? impedance matching issue with the battery?