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Lipo Lifespan?

945 Views 17 Replies 11 Participants Last post by  johnny b
It's probably already been covered here, but I can't find it.

How long do Lipo's last? I've got a 2S1200 Kokam I built myself about a year ago, that doesn't seem to have enough poop anymore.

Is there anyway to test them?
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I would like to know as well???
I don't know..I guess you could hook it up to a motor you knew would draw more amps than it could deliver even on it's best day and see how many amps it'd deliver at it's rated level, and how low the voltage got at it's rated discharge. Then fly it normally and see how much it'd take back in.

I've toasted an Etec just won't put out anymore. Some of my old Etecs are holding up good, some not so good. They'll all fly a foamy fine, but they won't lug that dang Axi around anymore. :wink:
I have an Orbit charger that tells me how much I am putting back into my packs. I have a couple Kokam 1500s that when they hardly fly the plane anymore will only take about 800 mah to recharge. When new they took 1400-1450. They don't have near the punch of my E-tec 1200s either. They used to!
I have heard hundreds and hundreds of charges as a number thrown around. Any rechargeable battery can last for many, many years if you store the battery in an "uncharged" condition like you received from the factory. The issue is that most of us stop and forget about them and thus they are left fully charged. In their fully charged state the battery has to work "against" entropy. Think of a battery having to do its "most" work to "stay" charged. If you uncharged the battery before long term storage, it will come to an equilibrium state and store the least "reactive" at that state.

It sounds like they are done.
I read somewhere on RCG that Lipos lose capacity over time whether they are used or not. I think it was something like 20-25% in a years time. All the Lipo mfgs recommend storing at 50% charge. At least that is what I have read on most of their sites.
NEVER STORE a lipo in the uncharged state, think of them more like a lead acid battery which if it goes to the uncharged state you will never get it back, lipos should never be left to go dead, because then they are really dead. :D
They say 600 cycles as a rule of thumb with proper operation.
I have talked with several LiPo manufacturers and they do test like this on all their batteries. I'm hearing from 500 charges up to 900. I'd say 600 charges is a safe number.
No, I wasn't referring to completely dead. If you let a NiCad go complete dead, it won't charge either...I have done that. You won't them as close to equilibrium as you can.

Is there an effect on Temperature on LiPolys? Like if you set the LiPolys in the freezer for say 3 months...what effect does that have on them?
I really don't think that putting lithiums in the freezer would be a good thing...but I'm not sure. Which leads me to a question....I fly when the temp dips below 0 deg F. I'd like to know the answer to this one too.
Pretty sure the lipos have a minimum and maximum temp.. I know guys who fly in the cold report a drastic reduction in power, some keep their packs warm under the car heater until ready to fly. The electrolyte is water soluble, I'm not sure if freezing would cause crystals to form or anything, I think room temp is a safe bet for storage.
Operating temperature
As we approach the maximum discharge capacity allowed for any given cell, temperature starts to play a prohibitive role. It is important that we do not exceed the maximum allowed temperature of about 80°C (140 to 160°F) or you will be heading for disastrous consequences.

An important comment here is that John L has on several occasionas published the value of 150°C as the critical temperature. This is well above the boiling point of water and few electronic components would survive long near it. For interest, extracted from JL's teaching knowledge, 60°C is about the highest temperature your fingers can tolerate, so 80°C will give you quite a burn!

Above the "critical temperature" there is a point of no return where "thermal runaway" occurs. Exceed that limit, and no amount of cooling is going to avoid a cell bursting into a ball of fire.

There is a flip side to the temperature issue though. The lithium polymer electrolyte does not like the cold. Its performance increases quite substantially when it operates within certain limits. It has been recommended that battery packs be kept out of the winter cold until they are used. This applies to storage as well. It has also been noted with interest, that multiple cell packs work better than one or two cell packs. The heating of the cells actually helps the other cells within a pack, providing of course you stay within the prescribed limits!
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I need to put my pack on a meter and see what it's doing.

I've used this pack for about a year now, but I don't think I have anywhere near 600 cycles on it. I'd be surprized if it had 100 cycles.

I've used this pack on my MGB, and a little indoor heli. It just seems to be getting weaker, sorta like it has developed a memory.

The pack has never gotten hot while being used. And it has never been charged over a 1C rate.
Harry, it sounds like you are in the same boat as I am. I had an TPs do that, and after bending Chuck's ear a while, he explained that my new Razor 350 was actually able to draw more amps than the Himaxx by a lot and that I probably toasted it that way.
Yeh, the lipos don't seem to tolerate much abuse at all. Thats why I have been trying to be very kind to mine....And, I would say they are getting better and better instead of worse.
Great thread. I've been wondering these things myself. Especially the cold issue, as I'm in WI and usually get in some flying all winter. Hope to fly mostly indoors, but if there's no wind and daylight it might be easier to head down to the park.

Real world, ran some Kokam 2s1500 (1st gen, not 2nd gen) into the ground after about 300 charge cycles each. This was really hitting them hard. At the end, they would charge minimally, and would run the plane for a couple minutes max before LVC kicked in. I know I'd run them too low at least a couple times each using a brushed ESC and brushed crap at the time, otherwise they'd probably have lasted much, much longer.

I've had my two TP 3s1320 2nd gens up for at least 150 cycles each, they feel brand-spanking new.

I think Billy's right on the money with that 600 cycle mark if you're running the newer batteries with 10C ratings, keeping them within specs (or close enough, lol). If so, that's the cheapest damn amount of legal fun I think you can get away with before they'd haul your ass off to the clink for some reason or another.
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