7 If you don’t have access to a load tester, turn the headlights on for two minutes or crank the engine for 15 seconds with the ignition coil disconnected. Voltage should hold around 11-12 volts. Anything less than 9.6 volts is unacceptable and not enough to start your engine. Ideally, your battery will maintain 11-12 volts with the load. If it drops quickly below 11-12 volts, it should be replaced. This Optima battery holds a steady 11.9 volts with the headlights on and the engine off. Of course, without the engine running and alternator charging, voltage would drop over time. It’s a matter of how quickly it drops that determines battery integrity.