Piaggio mp3 mix the battery terminals mistake

[Denisprygulea]

Unfortunately, I mix the battery terminals on my maxi scooter because the plus and minus symbols were not visible. I heard a click at some point and all-electric systems went crazy. After realizing the mistake, my scooter starts and stops just fine but after about 1 hour the battery goes dead. I check if the scooter is charging the battery but it makes only 8/9 volts. Does someone have an idea what the problem can be?
THNX!