Signs that your (insert brand here) lipo pack has reached it's usufull lifespan:
1) Lipos generally don't degrade much if any at all over the normal 300+ cycle lifespan (you'll see more or less cycles depending on the brand). So... if you notice anything "it wasn't doing before" it may be time to give it a serious look.
2) Ending temperature
As a pack reaches the end of the line, it's internal resistance starts climbing rapidly with each additional cycle. The first observed result is usually a hotter pack at the end of a run. It's working harder to supply the juice, so it gets hotter than you're used to seeing.
3) Output performance
Another commonly observed result is that the pack just doesn't have the rip it used to. Internal resistance again, and as it increases the pack can't deliver the same amps it used to.
4) Reduced capacity
I make sure and get a "baseline" for pack performance soon after the 20th cycle (fully broken in pack). I record starting and finishing temps on a test vehicle, the ESC and settings used, ambient temps, and driving style/venue used. I also drive the pack all the way to the correct lipo cutoff on the ESC, and then measure the Mah the charger puts back in. Every hundred cycles or so, I do all the above again and look for differences (warmer pack, less Mah in, less power and etc.). All packs are a little different, so sometimes I'll catch a pack with less rip, or higher temps, or less Mah in than before - there's not one or another that always comes first. But looking at Mah back into the pack once you have a baseline for it is the easiest way to judge the overall pack health.
One of the main points about all this is here: Once a pack starts going "downhill" it will continue to underperform, get hot, and not take full Mah in on a steepening downward spiral with each cycle. So it's best to immediately stop using and dispose of properly a pack you're sure is on a steep decline. A "just barely alive" lipo pack can sometimes fool chargers and cause a safety hazard if they are continued to be used.
Point taken and I agree! I'll shake somebody down to have more/bigger ones made
Core pack cycles:
I continue to race, test other things with, and in general put on as many cycles as I can on the original CORE 5000 1st production pack I have. I have just under 300 cycles on it as of today, with zero degredation so far from the day I got it. This one's been used and abused as hard as I can run it under normal circumstances, so when it decides to slide it will represent a bare minimum cycle life expectation for these packs. With my previous experience with lots of different packs, this one is looking like it will end up to be a good 400-500 cycle pack.