Lawn Mower Repair - Checking the battery
To start with not all mowers have batteries, so if yours doesn't skip this step and go onto the next step.
This is a quick and simple one to check but you will need a volt meter or multimeter. If you don't have one, get one, they are a cheap little tool that every toolbox should have.
Now this is as simple as it gets. Switch the multi-meter or voltmeter on and select thing selecting to pick up voltage in the 10-20 volt range. Place the black probe from the multi-meter on the negative terminal of the battery and the red one on the positive and read the voltage. You are looking for a voltage of about 12.6 volts. Don't be caught out by a reading of 12 volts, when a 12 volt battery reads 12 volts is is pretty much dead. If your battery is low charge it, leave it to for a day and test again. It the voltage has dropped off again your battery done and you need a new one. If the voltage has remained then the problem has been fixed.
Has this fixed the problem? If this hasn't try the next step.
