These are the ones I used before. I see they say discontinued??? Maybe they make an alternative.
I know you said you checked and charged the battery, but maybe try a different one, if you have one.
I have seen batteries that seem to charge up, but have very little power (amps), more like a surface charge
and die out quickly.
https://hobbyking.com/en_us/turnigy-...reduction.html

Shad