This is an easy check if you have a cheap, simple volt meter. It's much better to have an old fashioned needle meter rather than a digital. The needle is more sensitive, much quicker, and makes a clearer diagnostic tool. But not to worry, for you fancy folks a digital still works (sometimes the results are not as clear).
- Set the meter to DC Volts.
- Attach the red and black leads of the meter to the positive and negative posts of the battery. Most modern day digital meters don't care if the polarity is correct or not. However, if you have a needle meter, best to put the positive of the battery with the red wire of the meter; otherwise the needle will not be happy with you.
- Note voltage. It should read near13 volts if the battery is good and fully charged. If it reads below 12 volts it needs charged or it has bad cells. If after charging a few hours, the voltage is still below 12 volts then the cells are bad, replace it.
- Turn the key to crank the engine while keeping your eyes on the meter. Whether the engine cranks or not, the meter should not fall much below 11 Volts. If it falls below 10 volts or worse yet below 9 volts, the battery has a bad cell or two. Replace the battery, charge it, and repeat the test.
- If the engine starts, rev it up and watch the meter.
- If the charging system is working the voltage on the meter should quickly rise above 13 or 14 volts.
- If it rises up strongly towards the 14 volt range this indicates the charging system of the machine is working.
- If it plays around down near 12 volts you are reading the recovered voltage of a good battery, but the charging system is not working.
- If it simply stays below 11 volts, the battery and the charging system are both suspect. Replace the battery first. Fully charge it, and then repeat the tests before worrying about the charging system.
Note:if the battery falls below 9 volts the fuel cut off, a black cylinder on the bottom of the carburetor (if your model has this), will cut off the gas supply to the carburetor.