Battery Or Altenator

I would look at the battery first. Charge it, then start the bike check its charging. stop the bike check wether the voltage is dropping with ignition off, leave it over night see what he voltage is the next day. Or just replace the battery and see if that cures the problem.

 

Batteries can die suddenly. Sounds a bit like a loose or damaged cable could also be the cause. If you have a test meter checking charging system is a minute's job

 

The battery on my one year old T120 failed with very similar symptoms. It appears that due to space restriction these bikes use batteries which don't have a lot of spare capacity - interestingly my local dealer fits Optimate charging cables to all new twins they sell.

If you can get it started, with a jump, then check the voltage across terminals, you should get a reading around 14.5v (give or take) if the alternator is charging. You can also check the static voltage with the engine off, this should be around 12.2 to 12.5 volts. The last basic check is cranking voltage, check this across the terminals when you press the started, if it falls significantly below 11.5v then it is likely your battery is goosed.

If you fit a new battery then consider using a battery tender to maintain it when not in use. These bikes have a low but steady load on the battery when parked and over time this coupled with a marginal battery capacity will cause issues if a tender is not used.

 

I had a very similar issue with my 2019 Speed Twin 1200 back in 2023 with 12k miles on the clock. Fitted a new battery and that solved it.

 

I agree with the above, check the battery voltage, if it below 12v the battery has less than 30% of the original healthy capacity.
My Speed Twin 1200, Goldwing and car all live on Optimate battery charger/maintainer. It saves time, money and trouble in the end.

 

You need a volt meter to see what the battery volts are engine running....at idle it should read around 14v.
Have you charged the battery.....only charge with a low amps motorcycle battery charger...if you use a std car battery charger you riask cooking the battey.

So if you charge it is it ok for a while????

So few things to think about there.