How to tell when a LiPo is at end of life?

[mdavister]

I got a used heli (Honeybee King) that came with a lipo battery. Upon putting in my brushless setup, the ESC goes into soft cutoff after just a few seconds of spinning the rotors. Getting fed up with that I put my meter on the heli and got this: around 11V (3S pack) at 0 amps, but at 8 amps of draw the voltage falls to around 6 or 7 volts. Measurements were taken right at the battery side of the connector. Looks to me like the LiPo either can't handle 8A discharge, or it's dying.

The battery has not puffed up, and still looks physically great. Charges well and balanced to 4.2V / cell +/- 100mV. Anyone else seen anything like this? I have no idea on cell quality or ratings, my best guess on size is 800mAh-1000mAh, and since it came with an RTF, probably only 8C at best.

Another question:
If it is bad I'm going to replace it, but can't figure out if I want another LiPo, or take a step back and go with a Nimh pack. I like the safety of the Nimh, and the cost is much better, yeah flight times are reduced, but not a bad thing when learning. Thoughts?

Mitch

[poerqwa]

I think you answered your own question.
If you can live with reduced flighttimes stick with the nimh.
In a while the lipo's will probably have become cheaper as well so another benefit :)

I fly a lepton and consider the pack on it's way back when it takes less than 80% of the rated value.

Greetz,

Marc

[catfight]

mdavister,

Have you read info on the A123 batteries? Amp deliverers for sure. 4S of A123 batts about = to 3S Lipo. Several threads about these batts on rcgroups.
Cheap (sort of) and long life :D