I emailed optima about their chargers. Both are 12V only, according to them. They don't sell a charger for use on the 6V. Mike
I have five Optima batteries, (3) 6V, (2) 12V. I normally don't need to change them with any type of charger, except for the charge the get when I'm running the engine or driving the vehicle. If/when I do need to charge them outside the vehicle, I do not use a wall mount trickle charger.