Some lawn mowers have a charging indicator built into the dash or an “Amp Meter” as they call it. This is a meter that is connected in line with the engines charging system and will give you a visual clue as to what is happening with it.
On the amp meter, you want to see it reading in the 13.7 to 14.7 volt range to ensure that battery is property charged. A fully charged batter will have somewhere around 12.7 volts and could be higher depending on the condition of the battery.
If you do not have an amp meter, a simple volt meter test can be performed. With the engine running at full RPM and nothing running on the mower, place the positive lead on the positive terminal and the negative lead on the negative battery terminal and it should read be in the 13.7 to 14.7 volt range. If it is not or if it is reading higher, your alternator or the associated wiring is faulty and will need replaced or repaired.
You also should perform a test of your battery to see if it is still good and that the acid levels are correctly filled. A lawn mower batter today will only last about 3 years before it needs replacement.
If you need help troubleshooting why your lawn mower battery will not charge, visit our Locations page for a professional near you.