How can I tell if my battery needs to be replaced?

You should replace the battery, if one or more of the following conditions occur: If there is a .05 (sometimes expressed as 50 “points”) or more difference in the specific gravity reading between the highest and lowest cell. This means the flooded battery you are testing has a weak or dead cell(s). If the battery will not recharge to a 75% or more state-of-charge level or if the built-in hydrometer still does not indicate “good” (usually green or blue which is 65% state-of-charge or better) then the battery should be replaced. If a digital voltmeter indicates 0 volts, you have an open cell and you should replace the battery. If the digital voltmeter indicates 10.45 to 10.65 volts, you probably have a shorted cell or a severely discharged battery. A shorted cell is caused by plates touching, sediment (“mud”) build-up or “treeing” between the plates. If the battery is fully charged or has a “good” built-in hydrometer indication, then you can test the capacity of the battery by applying a known load and measuring the time it take to discharge the battery until 20% capacity is remaining. Normally a discharge rate that will discharge a battery in 20 hours can be used. For example, if you have an 80-ampere-hour rated battery, then a load of four amps would discharge the battery in approximately 20 hours (or 16 hours down to the 20% level). New batteries can take up to 50 charge/discharge cycles before they reach their rated capacity. Depending on your application, batteries with 50% or less of their original capacity are considered to be bad. I think that batteries that do not reach 80% of there original capacity should be replaced. If the battery passes the load test, you should recharge it as soon as possible to restore it to peak performance and to prevent lead sulfation. Always consider the temperature when making your evaluation and that the batteries are being properly charged.