See Also: Hummer H2 Bad Alternator Diagnosis A new alternator will rectify the problem. If you see your H2’s battery light turns on while the engine is already running, that is a strong indication that the alternator is no longer providing enough wattage to power the various electrical systems and charge the battery at the same time. A bad battery usually makes itself known when you are trying to start the vehicle.Ī bad alternator will usually make itself known when the engine is already running. It can run off the alternator just fine once it’s started. The battery is primarily there to start your H2. There isn’t a lot to it, which makes diagnosing it relatively simple. The engine turns the alternator, which charges the battery. The charging system in vehicles hasn’t changed that much in the last 50 years. That would indicate a bad battery, but it’s still worth your while to have it tested first. You may have noticed your H2 struggling to start, and then the battery light stays on after the start. With an older battery, you will often notice this on the first truly cold day of the year. Most battery lights will come on when the vehicle starts if the computer has detected that the voltage was too low for a quality start. The battery light comes on when it detects that the voltage in the battery is too low. It’s almost always going to be caused by a bad battery or alternator. The charging system itself is relatively simple. It is trying to warn you that there is an issue with the charging system. If your Hummer H2’s battery light is on, it means a few things.

H2 battery spy