Potensic D80 thinks battery is dying when it's not

[Flammarion]

I bought a Potensic D80 off of eBay and it's worked fine for a year. A few weeks ago I launched it and in about 30 seconds the low battery warning started beeping. I re-charged the battery and tried again and it did the same thing.
The battery indicator on the controller says it's fully charged, but drops a bar quickly after launch, then another and another. So I'm thinking the battery has gone bad and bought a replacement off of Amazon.

The new battery showed it was already 3/4 charged when I received it so I didn't charge it. I just tried it out and it did the exact same thing. I'm guessing the batteries are fine because what are the odds that two of them are bad. So maybe something in the drone is making it think the battery is dying? Or it's shorting out or something and draining it rapidly?

Thoughts? Thanks.

 

[NGO]

When I connect the 7.4v LiPo charger to the balance charger, the green light flashes momentarily and does not do that again. I have tried pushing the connector in to make sure its making all the proper contact to the 3 prongs. Now does the connector have to be flush against the body of the balance charger? Mine does not though I am sure it is not upside down because it's scored in such a way that you can only insert the plug in one way. I cannot imagine the battery is gone, or that the balance charger itself is bad. I guess I have to bring out the voltmeter to see if anything is being outputed from the BC of the battery pack is dead. I'd hate to buy anything I don't need

 

[NGO]

WHY IS THIS NOT WORKING, IT IS FAIRLY NEW MaximalPower 1PC 7.4V 3600mAh

 

[DoomMeister]

What balance charger are you using? Most chargers require a balance board for batteries that are less than a 6S (7 balance leads). Your battery is a 2S battery with only 3 leads. When connecting the balance leads the black wire (most negative lead for the pack) needs to be matched to the most negative pin of the balance charger’s balance port. It can then determine how many cells are present by where it sees voltage on the other pins. When balance charging the main leads also need to be connected to the charger.