Lipo storage, slight swell

[MattyB]

PS - The other important point about storing at full charge is the safety issue. Should an internal short occur through dendrite growth or the pack be damaged by an impact there is a huge amount of energy to be dissipated in the resulting fire, enough to self sustain it for many minutes. By contrast a pack stored at 3.8-3.9V/cell will merely fizz a and produce a small amount of smoke even if severely damaged.

[John Lee]

I have a 96S(!) Li-Ion battery in my plug-in Toyota Prius, not quite the same chemistry as a LiPo but the handbook gives similar advice:

■ Capacity reduction of the hybrid battery (traction battery)
The capacity of the hybrid battery (traction battery) will decline gradually when the hybrid battery (traction battery) is in use. The rate at which it declines will differ in accordance with environmental conditions and the way in which the vehicle is used. Observing the following can help suppress battery capacity decline.

●Avoid parking the vehicle in areas with a high temperature under direct sunlight when the hybrid battery (traction battery) is fully charged.

●Leave a low level of charge in the hybrid battery (traction battery) when leaving the vehicle undriven for a long period of time.

[Brian Cooper]

My Lipos are subjected to some serious abuse. High demands are put on them in EDF jets and other high performance models. They get no mercy, but the batteries have high "C" ratings and they generally cope quite well.

Whilst I appreciate the perceived wisdom of putting Lipos into storage mode, the fact remains that they die fairly rapidly if this is done. It is not just me, others have observed the same result.

It's a funny old world sometimes, eh...

B.C.

Edited By Brian Cooper on 28/12/2017 19:53:02

[tigerman]

This is very interesting but It has left me totally confused (that is not hard to do!)I used to charge my lipo to fully charged after my days flying and left them fully charge ready to go the next time I went flying but was told it was not a good practice and you should leave the batteries in storage mode and charge them up just before you go flying So what is the best leave them in storage mode or leave them fully charged.I must admit that when I left them fully charged up ready to go .I had no problem and might go back to that after reading this thread

[Bob Cotsford]

If my garage hasn't burned to the ground by then I'll let you know in Spring 2018 as all my batteries are currently stored fully charged and out in the cold . I suspect that over discharging them by ignoring the flight timer has killed more of my LiPos than has storing them fully charged.

[Stuart Z]

Posted by tigerman on 28/12/2017 20:21:53:

This is very interesting but It has left me totally confused (that is not hard to do!)I used to charge my lipo to fully charged after my days flying and left them fully charge ready to go the next time I went flying but was told it was not a good practice and you should leave the batteries in storage mode and charge them up just before you go flying So what is the best leave them in storage mode or leave them fully charged.I must admit that when I left them fully charged up ready to go .I had no problem and might go back to that after reading this thread

I agree, I don’t use my lipo’s very often, often months go by. They are up to 3 years old in some cases and get charged back to storage levels and have no signs of puffiness at all, (3S 2200mah) -however, I’m wondering if that is the correct procedure. I store them in a Bat Safe to reduce my concerns about them and only charge at 1 amp. Not knowing much about lipo’s, this thread has confused me a lot. Seems glow motors are much easier and safer and less confusing!

S

[tigerman]

Yes I am going back to leaving them fully charged and ready to go .Makes it more convenient when you want to go flying and not have wait hours waiting for your lipo to charge up

[Former Member]

[This posting has been removed]

[Dane Crosby]

I came back to model flying about three years ago. I went electric and obtained most of my escs, motors and LiPos from Purple power. I have operated the batteries in accordance with George's LiPo data sheet and never had a problem with them......apart from destroying the occasional one in a major collision with the ground.

A good reliable charger is a must though.

The sheets are available to download, free of charge (oops, a pun), from the purple power web site.

Edited By Dane Crosby on 28/12/2017 21:09:35

Edited By Dane Crosby on 28/12/2017 21:11:03

[Former Member]

[This posting has been removed]

[MattyB]

Posted by Brian Cooper on 28/12/2017 19:52:06:

My Lipos are subjected to some serious abuse. High demands are put on them in EDF jets and other high performance models. They get no mercy, but the batteries have high "C" ratings and they generally cope quite well.

Whilst I appreciate the perceived wisdom of putting Lipos into storage mode, the fact remains that they die fairly rapidly if this is done. It is not just me, others have observed the same result.

Once again, please cite some actual sources that support this observation with a plausible scientific explanation for it, otherwise it is just confusing supposition.

[MattyB]

Posted by Bob Cotsford on 28/12/2017 20:30:02:

If my garage hasn't burned to the ground by then I'll let you know in Spring 2018 as all my batteries are currently stored fully charged and out in the cold . I suspect that over discharging them by ignoring the flight timer has killed more of my LiPos than has storing them fully charged.

Just because they have not experienced a catastrophic failure does not mean you have not reduced their capacity and/or ability to deliver current by long term storage at elevated SOC. You would need a comparative test against a control pack to show that. You are right that over discharging is more damaging to a pack in terms of rapid degradation, but this is easily avoided by employing good practices (use of telemetry and timers etc).

[MattyB]

Posted by Tom Sharp 2 on 28/12/2017 20:46:33:

Posted by tigerman on 28/12/2017 20:35:03:

Yes I am going back to leaving them fully charged and ready to go .Makes it more convenient when you want to go flying and not have wait hours waiting for your lipo to charge up

 

Or you can get up at 4 am and start charging from storage level.

...or just get a good server PSU, high capacity charger and parallel board and charge all the batteries you need for an afternoon in ~1hr as I do.

Edited By MattyB on 30/12/2017 02:22:07

[MattyB]

Posted by Stuart Z on 28/12/2017 20:31:06:

Posted by tigerman on 28/12/2017 20:21:53:

This is very interesting but It has left me totally confused (that is not hard to do!)I used to charge my lipo to fully charged after my days flying and left them fully charge ready to go the next time I went flying but was told it was not a good practice and you should leave the batteries in storage mode and charge them up just before you go flying So what is the best leave them in storage mode or leave them fully charged.I must admit that when I left them fully charged up ready to go .I had no problem and might go back to that after reading this thread

I agree, I don’t use my lipo’s very often, often months go by. They are up to 3 years old in some cases and get charged back to storage levels and have no signs of puffiness at all, (3S 2200mah) -however, I’m wondering if that is the correct procedure. I store them in a Bat Safe to reduce my concerns about them and only charge at 1 amp. Not knowing much about lipo’s, this thread has confused me a lot. Seems glow motors are much easier and safer and less confusing!

There is no need to be confused. Charging lipo packs to 3.8-3.9V/cell is unequivocally the safest way to store them (there is far less energy in the cell in this state in the event that something does go wrong and a fire starts). There are lots of sources that provide an explanation and proof of this, including videos of people putting nails through packs that are fully charged (explosive, not recommended!) and storage charged (normally nothing more than some mild fizzing and a bit of smoke).

Re: degradation at elevated SOC, again this is a well researched phenomenon and there are lots of sources online that explain the science behind it - I linked a couple earlier in this thread, but a quick Google will unearth many more. If you don't believe me visit the RCGroups batteries and chargers forum where the world experts on the handling of lipos for optimum life and performance in RC tend to post; some have conducted testing across hundreds of packs and thousands of cycles using controlled testing methodologies to ensure results are fair and comparable. There is a good sticky thread on Lipo storage there with multiple examples and lots of questions answered which is well worth a read.

At the end of the day it is up to you to decide how to treat your batteries. However, before you decide it is worth critically evaluating the opinions being expessed and asking yourself which are backed up by credible scientific data. We can all "observe" the performance and cycle life of our own packs (including me!), but ultimately the sample sizes and number of cycles we are putting on our packs as individuals are very low, so our personal experience is not necessarily a true reflection of what is going on. Most critically few (if any) of the other variables that affect long term pack health will have been controlled, so comparing one persons results with those of another are unlikely to result in an apples with apples comparison. This is why I put far more credence on the research done in academia and by the battery industry in general than online forum threads, though some of the large scale testing threads on RCGroups have been very carefully conducted and can give some excellent insights.

Edited By MattyB on 30/12/2017 03:00:08

[Allan Bennett]

I'm with the "storage charge" school in this matter, except that I usually store at whatever charge they end up with at the end of a flying day -- usually just above 20%. I only store at 50% if for some reason I haven't used a charged battery that day, and have to discharge it.

I can't match MattyB's record of age and number of flights, though my oldest pack at the moment is a 6S 2600mAh Align 25C pack that goes in my T-Rex 500 heli (7-minute flights, so average less than 9C amps draw) and is now 8 years old with 160 flights on it. I did reduce my normal flight duration from 8 minutes to 7 minutes after the first year, but apart from that haven't noticed any performance reduction. I always charge at 1C.

Charging when one wants to fly is a hassle but, for me, the biggest argument in favour of storage at 50% or less is the reduced energy available for a fire. Batteries are so (relatively) cheap these days that the price of replacing them if they've degraded is not such a burden as it used to be, so perhaps longevity is not an issue for many people.

[Former Member]

[This posting has been removed]

[Allan Bennett]

Posted by Tom Sharp 2 on 30/12/2017 21:19:12:

I bought some graphene batteries from Hobby King recently, the instructions say. Shipped at storage charge, charge to full capacity as soon as possible.

All the Turnigy batteries (not graphene) I've bought in the past year or so have come at about 30% charge, which I believe is industry standard to reduce the risk of fires during shipping. Maybe HK want you to charge them immediately in case they've self-discharged further during shipping and while stored at a vendor. They don't say anything about storing at full charge, do they?