I wanted to test the battery from an e-bike. I have noticed quite strange behavior. The first thing I did was to measure the voltage. It was 66.1V which is fine for a 60V battery. When I connect the battery to the DC load the battery voltage drops to 58.2V, which is about 8V less. When I try to sink 0.1A - I can't. The maximum current I can draw is 0.01A and voltage drops to ~ 5V.
Fine, I thought, the problem is in the DC load. I connected it to battery charger, which sources 60V and about 2A. The voltage was correct and I was able to sink 2A.
Ok, so maybe battery isn't right - but then how come I can measure it's voltage and it's the same as fully charged battery? I tried to measure the battery voltage at the DC load terminals, and indeed it was ~58.2V. Last thing I tried - I have connected current meter as well to see which current is sunk when connected to load. That was 0.01 mA or 10 uA.
One last thing I tried - connecting 60W lamp to battery. Result - nothing, lamp won't light up. So likely either damaged battery or BMS.
Still, I'm wondering how such behavior can be explained. The only thing I can conclude - the battery is almost dead, the DC load sinks small amount of current and hence there's a voltage drop. Do you have any other suggestions?