Modern Vespa

Hello folks, noticed my battery was weak this morning so I decided to do some quick testing with my multimeter.

The scooter is new to me this year so I do not know the history of when the battery was replaced.

12.5V with the scooter off.
12V at idle

Slowly goes up to 13.5V on the center stand (takes about 20 seconds) with moderate throttle applied


If I disconnect the battery while the engine is running and just measure the output at the disconnected batter terminals it is 7 volts. Is this a valid measurement?

Don't disconnect the battery while running, on an alternator it will take out the diodes. Not sure if it will hurt the scooter charging system or not.

"If the battery is removed when the engine is running, the alternator usually keeps the engine running. Unfortunately, if you then turn off the engine without reconnecting a battery sometimes the alternator is damaged. This is because there can be a big voltage spike that would normally be absorbed into the battery, and instead the output diodes are damaged.

The risk of damage is higher if the alternator is delivering a lot of power, for example if the lights were switched on. Even an old battery which doesn't hold charge is better than running without a battery, and with an alternator setup you must have a battery connected to get the bike started.

Older bikes might have a dynamo generator, which can be started without a battery (by pushing and jump start, or with the kick starter) and they don't suffer the same damage as alternators when suddenly disconnecting the load without a battery present."

My old CT90, I know has a generator and they use the battery itself as the voltage regulator so it would blow light bulbs and such if the battery wasn't present.

It looks like the LX150 has a voltage regulator which I thought prevented things like that?

You can test your diodes by looking for AC current when the motor is running. If you get AC voltage, your diodes are fried.