EV scooter help!

Hi all, this is my first post so bear with me. I’ve got an 36 volt electric scooter that runs off 3 12V 12A batteries in series, but I can’t seem to get it to run. When it’s connected to the charger all the lights will turn on, horn works, turn signals work and wheel turns when throttle is applied. However, without the charger it’s a different story. I can get the horn to work but that’s it, no lights, no signals, no power to the wheel. I’ve tested the batteries with a multimeter and I know they’re good. Oh, and I have no idea of the brand, I think it’s some kind of Chinese scooter or something? Almost nothing is written in English. I believe everything is connected correctly, but there is an extra power type cord that doesn’t seem to have a home. Also, with the charger connected the bike will run even with the batteries pulled from the scooter. Any ideas, wisdom, or help of any kind would be greatly appreciated! Just trying to figure out more about my situation. Thanks!

With the batteries connected to the scooter - will the scooter run with the charger connected?

Thanks for the reply, yes it does run with the batteries connected and the charger connected.

Sounds like your batteries need to be replaced.