You never stated what the guy tweaked the regulator out put to. That Should be somewhere about 9.5 volts. Unless the 6 volt charger will puts out over 9volts it is not going to keep the battery up either.
I agree with most of the guys here 6 volts works fine as long as the cables are the right size and the regulator output is set at 7.4 volts. I found in the day that 8 volt batteries where just a crutch to get a guy by instead of rebuilding a "dragging" starter.
Another problem I have found is that most repairs are not made with the correct size wire and most after market wiring kits are not supplied with the correct size wire for the 6 volt headlights. I think that may be a two way street also since most comsumers fail to mention to the supplier of the wiring kit that they are planning to use it for a 6 volt application. Dim headlights due to small wire drastically increase the amps required to burn the headlights, thereby discharging the battery more than nessecary.
