We have been having lot's of discussions about the advantages and disadvantages of cheap Lipos versus expensive Lipos versus large versus small versus... you get the idea.  Folks, unfortunately we are generating lots of heat but not much light.  Thus in the tradition of the "Getting Amp'ed Up" forum, I propose that we collectively start posting FACTS about battery life that replaces estimates & speculation.  From what I have read a lot of folks are keeping good flight logs, hopefully we can share these about:

* the REAL size/weight/dimensions, not just what was published  Also C ratings
* cost
* application data like how the pack was used, how deeply discharged, how charged, temperature data (if known) etc
* any unusual circumstances - was the pack ever over discharged, crashed, frozen, overheat or...?
* number of cycles before they died.
" what kind of charger was used? charging rate?  Balancing method?  Balanced how often?
* Info on how you KNOW (knew) the packs were going south
* perhaps we do not need to sait for a pack to die.  Maybe milestones like "50 cycles still going strong" would be worthwhile?
* Anything else?

* Perhaps this could be a Sticky???

I hope that we can replace the speculation with some good old fashioned DATA.  However, based on what I have read I am not even really sure HOW MANY folks have actually worn out their Lipo's yet?  Real data may be scarce but I think we can set the table anyway...

FEEDBACK?  SUGGESTIONS FOR OTHER THINGS TO TRACK?

HI Dennis - This is a subject that is going to be very informative.There are two
things that I think impact Li-Po battery life besides using them in flight. I am sure
that some will disagree. The first is how you break in a battery before you fly it.
The second is how do you adjust the voltage when you store them between flying seasons.
These things may seem to have a small impact on Battery life  But I have noticed
some real performance differences over the lifespan of some of my batteries.

   
Walt Brownell

   

Since I have switched to the TP400 5S2P packs, I don't have any with enough time to "wear" one out. I'm at about 40 flights on the high time 4000 5S2P packs.

On my old packs, the TP 5S2P 4200 version, I wore the high time battery out after 120 flights. I keep log books on every battery for every flight, so I have the records. At flight 118 everything was perfectly normal, the discharge voltage, the charge mah, and the fully charged voltage. However, on flight 119, it slowed down "just" before the timer shut it off. Odd I thought. It was not too drained, and the balance of all the cells was fine. It charged OK, no imbalances or excessive mah input. On flight 120, it slowed down in the hourglass and limped it's way to the timer shutoff. This time, there was a cell that was WAY low on voltage. It was not apparent on the previous charge.  That was its last flight.

Please note that this was my FIRST LiPo battery ever. It was used for many different experiments, and not babied at all. In fact, it was discharges to within ~100 mah of its capacity, at least twice. There was NO break-in of this battery either. 

I have one more of these batteries with over 100 flights, but I have not flown the plane with these batteries for over a year now. The batteries have been sitting at 19.0 volts for that length of time...Just waiting for another chance..

I now "break" them in. I start at 1/4C and charge to full. Then I discharge. Then recharge at 3/8C to full, then discharge. This is repeated at 1/8C increments until I am charging them at 1C rates. Then I go fly them.

Paul Walker

I fly indoors in winter time with lipos, I store them for summer charged to 3,65V per cell balanced on charger for LiFe and then I put them to refrigerator

I do it several years and I did not find any visible difference after unpacking - measured capacity and internal resistance

Yes Jim, but those are not cells which we fly, A123 has after 400 cycles in my stunter much smaller degradation - for example I discharged 2150mAh from the new pack and 2000 after 400 real flights. And I know people having 1000 flight and still using them and they do not feel any need to change them (R/C guys)

Jim,
on these packs you have had go "west", what brands were they?
what Mah capacity were the cells,,
did you balance while charging and how often?
how far did you draw the batteries down when you were using them.
Information is only helpfull to us if we have ALL the parameters involved so that we can judge how it reflects on our usage
Please, share the rest of the info with us
thanks

Paul:

How do you discharge and at what rate (& to what level)?  Thanks.

I use a Thunder Power 1010C charger, and it has the option of discharging. I discharge at about 1/4 C.  It takes a while to get down to 3.8 volts/cell.

Paul

Dean
I agree on the capacity statement. I am trying 80% capaciity since my 1/2A planes are very weight sensitive. But the (Hyperion 3S 850 mah) batteries cost only $19 so I can afford to "burn out" one or two. So far they are looking good at 80% drain.

On the C statement I believe but cant prove yet that its the C that you use ralative to the batterys rated continuous C limit. The Hyperion batteries are rated 25C and I am using them at 10C to 12C. Thats only 50% of rated continuous current. Again time will tell how they work out at this load level.
Best
Jim

HI Guys- Here are some "facts" published in Quiet Flyer magazine in Jan 2007.
The best possible capacity retention for Li-Poly batteries is obtained when you store them half- charged and keep them cold around 32Degrees F. This results in a 2% loss of capacity per year. The next best is 4% loss per year when stored at 75 Degrees F.
Half charged = 3.81 volts/cell no load pack voltage
6S pack = 22.86 volts
5S pack = 19.05 volts
4S pack = 15.24 volts
3S pack = 11.43 volts

 When refrigerated a battery should be placed in a plastic bag to protect against
condensation.


I have been storing my 4S batteries since 2007 at 65-70 Degrees F   

Walt Brownell