Dennis, what timer are you using?

I've found Zippy compacts do tend to weaken in capacity and power, which I suspect is from having the internal resistance in the cells steadily climb till they're no longer able to deliver the punch you need, or the time you need, or both.

A change in speed is less noticeable on a governor timer like a KR, but you do find you'll get early shutdowns as the pack weakens.

1/ The simplest, quickest and probably the only possible is to buy new battery. You can see problem also if you measure internal battery resistance, if your charged allows it. Compare values with healthy battery and all will be clear.

2/ You can check what is the problem if you read voltage during flight from ESC, you will see if problem is really extraordinary low voltage, because:

3/ It could be that you use too low number of cells for your motor and prop. It needs some voltage reserve to allow proper working of governor. It can work well with new healty battery and it can fail if battery is older just by little voltage drop. If you have enough headroom it will work well also with older battery. So may be you can tell us KV of your motor and prop which you use. It will be clear if this is the case. If the voltage is "on edge" it can also cause nice level lap times, but will not pull well overhead, becayse governor cannot add power for climbing.

What I would like to get a handle on is how can we check the health of a pack as we use them? What can we easily measure and how to do it? Also, how can we store cells between flying secessions to minimize buildup of internal resistance and/or puffing?

Thanks,    DennisT 

This is a question that I would like to "piggyback" on.  Keeping batteries for 3 ships healthy is rapidly becoming a full time job for me.  My biggest problem is when I have 6-8 batteries charged and we don't fly.  I have no idea why but a flown battery will fully recharge in about 30min but it will take an hour to be put into "storage".  A fully charged battery can take hours to be "stored".  There has to be a better way.

Ken

That's because you are charging a 'flown' battery at, eg: 100 watts - 3 or 4 amps x 4 cells,  to about 1/2 charge.  Most chargers will only discharge a fully charged battery, to "Storage" voltage, at about 1/10th their charge capabilities - in the example, 10 watts or maybe .3 or .4 amps, from 100% down to 50%.  They don't have the power handling capability in "Discharge" mode as in "Charge" mode.