Voltage, and amps are two separate things. You can have 12.8 volts, and very low amps. So, if it is easy, go to an auto parts store, and have them LOAD test the battery.
I am far from a parts store, but I have nice jumper cables. So, I'd hook up jumpers, to a nice hot battery. Be extra careful with polarity, + to + and - to -. And, host motor NOT running.
And, see what happens.
Also, you can have BAD connections at either end of your battery cables. Remove and clean, and coat with a bit of grease, and you may find the amperage gets through.
Just my 2 cents.
N:boxing_smiley: