7.4v 4000 battery. I tried to use Onyx 230 to charge, say battery error? But i tried to use Hyperion charger, this charger charges it no problem.
My question>> bad charger or battery?
Thanks

Sounds like charger but check all your connections and try a different battery before condemning it .

Are you balancing or just charging?

I always ruin the balance lead on all of my connectors. When they start to fail, they show really screwy readings on the charger's end. 1 cell might be at .90v while the other is at 7v. I just swap out/repair the lead and all is well. Even if they look good, there can be an internal break in the wire.