Basic Information on Battery Voltage

Tips & Support
OPTIMA Batteries
Milwaukee, Wisconsin

We posted a very unscientific survey on the OPTIMA Batteries facebook page yesterday, hoping to get some idea of what folks are thinking when they hear the voltage level of a battery.  We stated that a 12-volt battery measured 12.1 volts and then asked if the battery was fully-charged, overcharged or needed charging.  

The first six votes were a mix between a battery being fully-charged and needing charging.  After that, the overwhelming majority (20-2) felt that a battery that measured 12.1 volts needed charging and they were correct.  We thought that might happen, as folks tend to go with the majority once one choice becomes clear.  We hope all of those who voted for the battery needing charging really understood that just because a battery is called a "12-volt" battery, that doesn't necessarily mean a voltage level of around 12 volts suggests a battery is fully-charged.  

The truth is, most 12-volt batteries need to measure at least about 12.6 volts before they are considered fully-charged.  That is because each of the six cells in a 12-volt battery should measure at least about 2.1 volts when fully-charged.  Multiply that number by six cells and you arrive at 12.6 volts.  Battery chemistry can vary from one battery to the next, so we say "about 12.6 volts," because a battery could be fully-charged at only 12.5 volts or 12.8 volts and some batteries may be fully-charged at even higher rates.

Our YELLOWTOP and BLUETOP batteries (except for the 34M BLUETOP) are fully-charged at about 13.0-13.2 volts.  If those seem like a lot of numbers to keep track of, we'll give you one simple number to remember- 12.4 volts.  If you only remember one voltage number relating to batteries, 12.4 is the number to remember.

Whenever any lead-acid batteries (including AGM batteries) are discharged below 12.4 volts, sulfation will begin to form, which diminishes both capacity and lifespan.  That makes a quality battery maintenance device, like an OPTIMA Charger or Maintainer, an excellent investment for any vehicle that doesn't see regular use. Whether you have one of our REDTOPs, a YELLOWTOP, BLUETOP or even a flooded battery, make sure you keep the voltage maintained above 12.4 volts whenever you can- especially when your battery is in storage.