I just bought a used P4 and it came with 4 batteries that would not take a charge or light up at all. 1. I removed the case on one and removed the balance cable 2. I did not disconnect the battery main leads but instead soldered to small lengths of solid core wire to the solder pads. Charged battery at 1A 15V for 30 minutes using my G.T. Power A6 Intelligent Charger on the NiMH setting which gradually ramps the current and voltage until it finds the nominal charging voltage of about 15.5V. The battery charged to about 14.78V. 4. With no charger - and balance cable still detached, I left it for 2 hours to allow the memory IC to deplete fully and erase the low voltage detection condition and reassembled it. The battery turned on!

The issue now is that LED 1 flashes 2x a second for about 5 seconds and then goes into a constant flash. When you try to turn it on, all 4 LEDs light up, but then it goes back to LED 1 slow flashing and it will not take a charge. Also, when I put this particular battery on the charging hub, it has a yellow indicator on the hub.

What does the flashing LED mean and what does the yellow charger indicator mean? Is it because this one has a bad cell? Is that why it will not charge to 15VDC?