I have used traditional Lead/acid batteries in all of my cars except the Charger. The lead/acid batteries seem to all test over 12.5 volts in the cars I have here. The Charger had a Red Top Optima until recently. It lost charge frequently and charging it was always a pisser since the gel-cell design had a unique charging procedure. ( I do not have a specific gel cell charger) Even when charged to the point where the charging unit shut off, it never got over 12.3 volts. Many times it read under 12. It has lost charge a few times lately so I decided to replace it. I had planned to get a regular lead/acid battery but the guy at NAPA convinced me that the AGM one he had would last longer as long as I put a slow trickle charge on it when I expect the car to sit awhile. The one I bought tested at 12.6 even after sitting on a shelf awhile. I also bought a small trickle type charging unit. At home, I charged a battery from my 67 Dart. Today it tested at 13.06 volts! What? I don't recall ever seeing any of my batteries test over 13 volts before! I put the charging unit on the new battery to see where it ends up. I have used Optima batteries in my '70 Charger since 2002. The starter never spun real fast but it was always enough to start the car. I can't start the car now yet though. I have the carburetor at a friends shop. I'm anxious though to see how it spins over with a better battery.