Modern Vespa

I'm about to see my 3.5y old GTS for the first time in 4 months. The battery is disconnected, so hopefully it hasn't discharged too much, but it's a pain in the ass to get to a storage unit without a vehicle, so I want to be prepared.

The only motorcycle shop that's open on Sundays is a CycleGear that is a bit out of my way. I'm wondering if I can have a friend with jumper cables meet me at the storage unit, so I can at least get my Vespa over the bridge and somewhere where I can check/replace the battery if necessary. I'm presuming I can ride it safely until I turn the key off so long as I can get it started.

I'm also presuming that any cables a friend might have would be car sized. Are they reasonable to get onto a Vespa battery while it's still mounted in the floorboard?

(I did search, but all the relevant posts looked way old and didn't talk about cable choice.)

While the battery is still disconnected use the jumpstart cables and the cars running engine to charge the battery for, say, 20 mins. Then connect and try.

Good suggestion.

On the cables: in general larger cables are never a problem in electricity.

2 years ago my BV had a flat battery, after a standstill of a lot of weeks in the winter. Just used the starter cables of my car, and my car to get the engine starting.

And as you say, once you get the engine started it will keep on running as long as you do not switch it off.

Those $40 lithium battery packs for starting cars with dead batteries are about the size of a shoe, and work fantastically with little Vespa engines. If the engine was running before you put it away, and you used stabilizer in the fuel, I would be surprised if you needed anything else to get going regardless of the condition of the battery itself.

I did not have a problem with standard sized cables when I needed a jump while on a trip (and the rectifier going tits up).

Best suggestion so far.

If you can somehow securely fasten the large clamps of the jumper cable and you want to jump start from the car: the engine of the donor vehicle should NOT be running.

Or hook the disconnected battery up to a car battery charger, but don't run it over 2 amps and keep an eye on it.

I love these things, I put one in each of our cars, much better that asking a stranger for an jumpstart. I borrow one to carry in the Vespa when the battery is acting dodgy. Also good for an emergency phone charger battery during a power outage.

I have cables designed for a car that will fit my GT200. Just make sure the positive cable does not touch the metal frame. As far as not burning up the cables due to high resistance, the bigger the better. But the clamps do have to be small enough to fit on the battery terminals with the battery in the battery compartment. As for leaving the engine running, the only real difference will be voltage. With the car engine off, the battery should have about 12 volts. With it running, it should be around 14 volts. The GTS charging system should also put out around 14 volts, so the Vespa should be able to handle that with no problem. As for amps, the starter on the scooter will draw only as much as it needs, no matter how much is available. The main thing is NOT to ground out the positive terminal of the battery. That can damage some very expensive electronic parts.

Those lithium jump starters are cool, and I have one that I carry with me on whatever bike I'm riding. But I am afraid of them. I've seen too many videos of lithium batteries catching on fire. A few years ago Samsung made cell phone batteries that would catch on fire. And it's an intense fire. Not a little flame like a cigarette lighter, it's more like an arc welder.

Correct, the problem is voltage spikes for both the donor and receiver vehicle. That's where a control unit tends to blow up in modern vehicles.

If you are lucky in bad luck, it's only the fuse: Possible electrical issues

Many newer vehicles have a separate positive terminal in the engine compartment that is protected against voltage spikes, and using this is safer than using the positive terminal of the battery. Ground should not be connected to the negative pole of the battery anyway.

Reconnected the battery and it started without assistance.

Let it idle for half an hour and then rode it for another half an hour. Hopefully the battery is in good enough shape to last the rest of my time in SF.

So, no problem at all.

I would not let it idle for half an hour. Better to start riding once the engine starts.
Your engine will be sooner on normal temperature which is better for wear and your battery will charge faster.

For $30 you can get a set of motorcycle jumper cables...
They fit great.