So I just recently bought a 2nd hand E-Bike. It is a Hybrid Trek 7.3FX with a Conversion Kit from RayBen Motors.

I bought this bike, and rode it 13km back to my home. When I did so, I used the electric motor in a fair usage, and got home with the meter still saying full charge.

I unplugged the battery and left it there for 2 days (off position) due to rain. After that, I decided to go out one night, so I plugged it in and it was yellow... then as soon as I went outside it went red and the throttle did not work. I figured that the battery drains pretty fast, so I thought I'd charge it.

I plugged in my charger into the wall and it lit up green. I plugged the charger into the battery and it still stayed green. Now there is a battery gauge on the battery itself and I clicked that and it says FULL when unplugged (although some clicking sometimes yields RED, as in 0). And I left it overnight. In the morning I plugged it back in to the bike and same thing. Red on the bike meter. So then I tried charging the battery while it was on the "On" position (not inside the bike). My results later were the same. I was confused whether this was a battery issue or a charger issue (since the charger showed no signs of changing lights). So I clicked on the battery gauge (on the battery) and held it. It read full. I plugged it into the bike while holding the gauge. Full. I turn the battery on. Red. Then I unplug the battery and try plugging the charger while holding onto the battery gauge button so I can see what it says. It says Full, then when I unplug it, it says Full. When I plug in the charger when its NOT connected to the wall it says Red. So I tried charging the battery while it is attached to the bike. Still nothing.

Finally in order to test to see if the bike has issues, I left the battery in the bike, plugged the charger into the battery and turned it on. The gauge on the bike read Full (for once) and the throttle worked, but only for a second and then the gauge went red. I turned the battery off, then back on again (full bar). I lifted the bike so there wasn't any force against it and hit the throttle and the wheel goes. It keeps spinning, faster and faster. So the motor works. Electronics on the bike works...

Next thing I notice is that while I hit the throttle, the charger LED turns RED (first time I saw it red! Seller told me it sometimes doesn't turn red, but I never saw it EVER turn red). This made me figure that it was likely not a charger problem.

My question is... what is wrong with my battery? I'm thinking there might be a loose connection or something, or the charger 'thinks' the battery is full so it is green (trickle charging?) and not really fully charging.

Considering my battery was able to last me the first 13km, and I was going at like 30 km/hr+ max throttle... to now absolutely nothing on my battery, I was thinking that there might be something that went wrong with the battery and that the battery isn't really actually dead itself. Or is that possible? To supercharge a dead battery to make it work in order to sell it off to an unknowing buyer (me)?

Thanks ahead of time!