I just bought my scooter 12 days ago and have not had any issues thus far. After filling up today, my scooter would not start

Luckily, I was at a 76 gas station that has a little mechanic shop attached. I asked one of the guys to check it out. He tried starting it and instantly said "it's the battery". I said "the blinkers and lights light up just fine." In that moment when he checked, they did not light up.
He removed the floor matt and connected a battery tender thing to it. He explained that the signal was very low. We charged it up for about 10 minutes (i had to rush home and get ready for work), tried starting it up, and it worked just fine. He recommended I buy a new one.
When I got home and turned it off I tried restarting it just to see if it would, and it did.
Now I need some guidance please! I live in an apartment complex with really no outlets in the garage where I park. The person I bought the scooter from told me he kept it on a battery tender as he was no longer riding it everday. I thought I wouldn't have an issue as I have been riding it everyday since I purchased it. I have not taken it out for long strolls. Mostly just running errands around town and what not.
Could it be that the battery is just old and done in and I need to replace it? If so, where do I buy one? I looked on Scooterworks, but found nothing. How long does a battery life last?
Or do I just buy a battery tender and try to find somewhere I can charge it up consistently? Its hard to do this in an apartment complex. Also, I did not think I would need to do this if I am riding everyday.
Any advice would be helpful!