Modern Vespa

Hello everyone,

I would like to get your opinion on my issue with Vespa LX 125 (2007) not holding charge.

Last week I fully recharged the battery and took it to work on Monday, Wednesday and Thursday. It is about 14km/9 miles one way. When I tried to start the scooter today, after 8 days of not riding it, I was not able to start the engine because of flat battery.

I bought a new battery last year (SIP 12V/10Ah, YTX12-BS).

I tested the battery and got the following readings

Engine turned off - 12.7
Engine off, with headlight on - 11.7
Engine on - 12.3
Engine on, revving at WOT - 13.7
Battery Fully Charged while trickle-charged - 12.9

Any idea what could be wrong? The battery, the regulator or maybe a short?

Remove battery from Vespa. Put on charge for overnight. Remove charger. Let battery sit for a week. Install battery in Vespa. Does it start engine? If not, then you need a new battery. If it does start, then you have an electrical problem in your Vespa (a short).

Based on the numbers at engine on, sounds as a charging problem. 13.7 at WOT is very small

A battery maintainer for a lead-acid battery should be producing 13.6V. Much less and it won't fully charge, any more and it could over-charge if left on after the battery has become fully charged.

The volts directly across the battery shouldn't go down to 11.7 with the engine off and the headlight on. This signifies a greater than normal internal resistance in the battery, and it probably won't start the engine when you try that.

At idle on a 125 or 150, anything above 12V is OK - but revving should produce 14.4V. More than 15V denotes a bad regulator.

This all points to a high internal resistance in the battery. High here means more than 100 milliohms.

I'd replace the battery - and these days I recommend getting an LiFePO4 (LFP) battery. They are now about the same price as good branded lead-acid, but won't let you down after a year!

nope

I would suggest you remove the battery, trickle charge it overnight and take it to an auto center/ parts store tomarrow and have it load tested. If it passes, then check out the relay and/or starter motor. If it fails, it's new battery time. How many miles are on the scoot?

Thank you everyone for the comments and sorry for such delayed response. I got busy and did not have time to further troubleshoot the scooter.

I ran a few more tests and followed instructions from this YouTube video (https://youtu.be/l20k6vFoz2Y?si=Ji95B5fcNbhzu1-w&t=439) and my multimeter was showing 0 Amp which should mean there is no parasitic draw.

My next plan is to get a new battery and test when the engine is on, revving at WOT, if it produces 14.5V. In case it produces significantly less than that, what should be the next course of action? Regulator, stator?

Thanks again!

Testing the stator! Easy to do with your meter. First check for continuity between all three wires, and their isolation from ground. Then check for >17V AC between each one.

Test the regulator with a fully charged battery, a couple of minutes after starting. >13V DC at idle, >14V but <15V when revved.

When you're happy with the results, stuff loads of dielectric grease into the big three-prong connector between the stator and the regulator.

Batteries are a pain in the butt. I have not had problems with the Vespa not charging adequately. In Minnesota, if they won't hold a charge, it is usually a result of freezing the battery.

I have avoided problems by keeping the battery on trickle charge when not riding.

Throw it away get another.

Bob Copeland

Hey, Bob. Sorry, but I thought keeping it connected to a trickle charger is a BAD idea. -No?

That does depend on the type of battery. Flooded, gel and AGM should be left to their own devices and just topped up now and again.

The fully sealed ones (often used for emergency lighting, weed-whackers and lawn mowers etc) can be left on a floating supply designed for the job.

I've seen so many batteries killed through being left on chargers - including Battery Tender Junior and even Optimate, which isn't quite as 'intelligent' as its hype.

I disconnected the regulator harness that is behind the horn cover and did some testing. I set my multimeter to AC voltage and tested all three yellow wires (tested all combinations).

10.8V - regulator was plugged in, engine was idling

28.3V - disconnected the regulator and measured all three yellow leads at idle
38.3V - disconnected the regulator and measured all three yellow leads while revving the engine

Do you think it could be the regulator that needs to be replaced?

Also measured DC voltage of the positive and negative coils in the regulator harness and it gave me the same readings as when directly measuring the battery itself, which was about 13.07V.

If that battery was a new one, and fully charged (so one would hope it's AOK), then 13.1V is far too low when revved - replace regulator. If that is the old battery, so called 'fully charged' then replace that first - and give the new one a top-up charge before first use regardless of manufacturers saying you don't need to (looking at you, Motobatt).