If you have a tractor, truck or other farm machine that constantly needs a boost to start, you need to determine whether it’s just time to replace the battery or if the alternator is not doing its job. There is a fast and easy way to determine which problem you have. All you need is a multimeter. Here’s how to do it.
With the engine off, set your multimeter to read voltage, then attach its positive and negative leads to the battery. The meter should read about 12.65 volts. That number will be slightly higher or lower depending on the age and condition of the battery.
Next, start the engine and take another reading in the same way. If the charging system is in good condition, the meter should read about 14 volts, indicating current is being fed back into the battery. If the reading is low, there is a charging system fault. †