Optima not only makes great batteries, but the company is an excellent source of battery knowledge, and its series of tech tip videos, such as the one seen above on how to know if your battery needs to be replaced, are a true educational experience. So whether or not your custom car, hot rod or tricked-out truck has an Optima battery under the hood, sit back, relax and learn.
Here are some quick tips on checking your battery’s condition, and a few things that may be causing it to discharge abnormally and give you problems. We hope this video and these tips from Optima Batteries help you become more comfortable with your car care and maintenance.
First of all, the typical fully charged starting battery, with the vehicle’s engine turned off, should measure (using a multimeter) about 12.6 volts to 12.8 volts. Deep-cycle batteries and dual-purpose batteries should measure approximately 12.8 volts and 13.0 volts. Voltage measurements of the battery when the engine is running are the output of your alternator. This measurement should be about 13.3-15.0 volts, which may differ due to temperature. At average operating temperatures of 50° to 80°F, your alternator output voltage should be about 14 volts to 14.8 volts.
If you don’t have a multimeter, test the output of your alternator by starting the car and turning on the headlights. If they are dim, that may indicate the lights are running off the battery and that little or no power is being produced by the alternator. If the lights get brighter as you rev the engine, it may mean the alternator is producing some current, but may not be producing enough at idle to keep the battery properly charged. If the lights have normal brightness and don’t change intensity as the engine is revved, it may mean the car’s charging system is functioning normally.
If that checks out, you want to determine if the battery is holding a charge, or if something on the vehicle is discharging the battery.
There are three likely scenarios to explain the problem:
- A high parasitic draw (key-off load). This can quickly discharge a battery and decrease its life. This may be caused by a trunk light, cigarette lighter, clock/radio, alarm system or any other electrical device. Drain on the battery can be checked with an ammeter. With the ignition off, disconnect one of the battery cables. Connect one ammeter lead to the battery and the other to the cable. The normal current drain should be about 25 milliamps or less. If the key-off drain exceeds 100 milliamps, there’s an electrical problem that requires further diagnosis. If you don’t want to take your car to a mechanic, the easiest way to isolate the problem is to pull one fuse at a time from the fuse panel until the ammeter reading drops.
- The battery is not holding a charge. To find out if it’s the battery or a system in the car, remove the battery from the vehicle, charge it to the full voltage, wait 12 to 24 hours then measure its voltage. Another faster, but less preferable way to do this is to turn on the high-beam headlights for 15 seconds, turn them off, wait 5 to 10 minutes, then check the voltage. If you measure the voltage of the battery the next day, week or even a month later, the voltage should be close to the max voltages listed above. If the voltage holds when not installed in your vehicle but drops when it is in your vehicle, see #1 above.
- The battery was somehow discharged, and your maintenance charger is not able to properly charge the deeply discharged battery. Please see the directions for charging a deeply discharged battery.