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Lipo Battery Storage

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RC Plane Flyer18/09/2018 18:38:44
654 forum posts
19 photos

I am looking for advise on Lipo battery storage . As the summer flying is coming to a reduction on visits to my local flying field and over the last few years having had batteries swell for unknown reasons, certainly not abusing them. Do I now leave them at the voltage I find the batteries are when I buy new and charge up the night before more than a full charge and maybe not use them for some weeks

Tom Sharp 218/09/2018 18:50:03
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3545 forum posts
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So cheap nowadays, it's hardly worth bothering storing them. cool  

Edited By Tom Sharp 2 on 18/09/2018 18:51:34

Biggles' Elder Brother - Moderator18/09/2018 19:13:17
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Batteries puff up for a number of reasons, but one of the major ones is leaving them in store for long periods at full charge. If you are not planning to use a battery within the next week or two I would take it down to storage charge (about 30-40%) this will go a long way to protecting it from puffing.

BEB

PS When was the last time you bought a Lipo Tom? £90 or a 6s 5000mAh now - 6 months ago the same battery was maybe £50! Batteries are expensive now - shortage of lithium!

Tom Sharp 218/09/2018 19:38:51
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3545 forum posts
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BEB

I bought twelve assorted HK Graphene batteries last October ranging from £30 to £50.

Must check on todays prices.

I don't go into the 6s range. Petrol seems a better bet at those sizes the way I fly.

bought a new li-ion battery for my Samsung galaxy phone the other day £3-50 delivered.

Edited By Tom Sharp 2 on 18/09/2018 19:43:20

Allan Bennett18/09/2018 19:43:13
1555 forum posts
39 photos

If I've charged a battery and haven't been able to use it, I discharge it back down to 'storage' voltage, which on my charger is about 50% capacity or 3.85v per cell. If I've flown a pack I store it at whatever voltage it finishes up at, which I know from experience (timed flights) is something in the range 20% to 25% capacity. I only charge the morning I'm going flying.

The only thing you have to watch out for is that the packs don't self-discharge down below about 3.0v per cell, at which point they might not be usable again. My experience with modern packs is that self-discharge is not a significant issue, even for storage of 12 months or more.

leccyflyer18/09/2018 20:00:39
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1271 forum posts
302 photos
Posted by RC Plane Flyer on 18/09/2018 18:38:44:

I am looking for advise on Lipo battery storage . As the summer flying is coming to a reduction on visits to my local flying field and over the last few years having had batteries swell for unknown reasons, certainly not abusing them. Do I now leave them at the voltage I find the batteries are when I buy new and charge up the night before more than a full charge and maybe not use them for some weeks

Generally accepted best practice for storage is to discharge down to around 3.85v per cell and keep the batteries in a fireproof container protecting them from freezing.

Stephen Smith 1418/09/2018 21:07:13
151 forum posts

5000 6s 30c constant 60c burst in stock at hobbyking UK and qualifies for free p+p only £49.85 and that's not logged in so possibly a couple of quid cheaper . So not that expensive only a couple of gallons of glow fuel.

Biggles' Elder Brother - Moderator18/09/2018 21:57:15
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Mmmm, yes a Turnigy, I have some of these; and examples:

One rated at 20-40C (bit vague!) actually can deliver 8.2C at best. Another (same rating) can deliver 14.2. These figures are based on the battery's internal resistance and potential heat generation damaging their chemistry even further.

These are not isolated expamples, I have some 3000mAh 6s Turnigy batteries which ae rated at 25C and bearly deliver 13C. Although to be fair some in this capacity class are better.

But my overall conclusion? I don't buy Turnigy high-capacity/cell-count batteries - you seem to get what you pay for!

BEB

Trevor Crook19/09/2018 07:15:39
864 forum posts
65 photos

I try to follow a storage regime in the winter when I fly less, but am lax in the summer.

RC Plane Flyer19/09/2018 09:19:25
654 forum posts
19 photos

Thank You for the responses and will have to get the charger instructions out and read up about the discharge option and see if it auto cuts out

Denis Watkins19/09/2018 09:44:12
3911 forum posts
61 photos

Am the opposite, as I fly I/C in the good weather , and having stored at 50% all summer, the Lipos now come out for winter flying and indoor.

On inspection of 50% stored lipos since March, non are swollen or down on voltage, so 50% seems a good bet.

Edited By Denis Watkins on 19/09/2018 09:46:10

The Wright Stuff19/09/2018 09:46:05
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1381 forum posts
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This argument has two sides, both equally valid. It depends upon the cost of your batteries and the relative value of your time.

Batteries will last significantly longer if they are consistently treated well. But monitoring charge and discharge cycles is time consuming.

If you are retired and have lots of high C 6S packs, then it's probably well worth taking care.

If you fly foamies with bog standard 2200 mAh 3S low C packs, then the relative reward for investing the time is much less.

I have a full time job, a two hour commute, and two young children to sort out each day. To have time to carefully manage my batteries, I would need to take a day off work every week, unpaid.

For that, it's much much cheaper to simply replace my batteries every couple of years or so...

So there we are, while technical information is useful, personal circumstance is relevant too...

Edited By The Wright Stuff on 19/09/2018 09:47:14

Biggles' Elder Brother - Moderator19/09/2018 11:23:10
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Fair point TWS. When I was working I too was a lot more casual about battery stoage - given a choice between spending a free afternoon flying or doing battery maintainance its obvious which you ae going to choose!!

But now I'm retired, a man of leisure (Ha!) I'm in the shed working on something most of the day (keeping out of the way!) so having some batteries winding down to storage or being charged up in te background is no big problem.

BTW I don't believe that the exact level of storage charge makes much difference. Anything from 50% down to 20% seems to be fine. So if you have flown the batteries you can often just put them aside to store as they are already at a suitable charge level. One tip, I have a jar of brightly coloured elastic bands on the bench, if a battery is at storage charge I stick an eleastic band around it, that way I can see in a glance which batteries are and which are not. Yes, I know I could just use a checker - but this is a bit faster and easier!

BEB

RC Plane Flyer19/09/2018 11:40:04
654 forum posts
19 photos

I am with Dennis an avide I/c flyer with the odd electric to fill in gaps so this could be the cause of the swelling. I have just replaced the battery stock and making sure I do not have the same problems of swelling . Thanks again for the responses and have downloaded the charger instructions and retire to the hanger to see what happens in a discharging set up.

MattyB19/09/2018 12:56:33
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1955 forum posts
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Posted by The Wright Stuff on 19/09/2018 09:46:05:

This argument has two sides, both equally valid. It depends upon the cost of your batteries and the relative value of your time.

Batteries will last significantly longer if they are consistently treated well. But monitoring charge and discharge cycles is time consuming.

If you are retired and have lots of high C 6S packs, then it's probably well worth taking care.

If you fly foamies with bog standard 2200 mAh 3S low C packs, then the relative reward for investing the time is much less.

I have a full time job, a two hour commute, and two young children to sort out each day. To have time to carefully manage my batteries, I would need to take a day off work every week, unpaid.

For that, it's much much cheaper to simply replace my batteries every couple of years or so...

So there we are, while technical information is useful, personal circumstance is relevant too...

All correct, but there is an important caveat - storing lipo batteries fully charged is significantly less safe than in storage. It's not just a drop in performance that occurs when storing at elevated SOC. Dendrites can grow internally which in extreme circumstances bridge the anode and cathode, shorting the battery and causing heat to build rapidly which then triggers a fire. This is why lipos are stored and transported at ~30% charge for distribution.

Yes it's rare, yes it probably won't happen to you, but it is a real, scientifically proven effect. At the very least if storing at full charge (or anything over 4V) regularly then make sure they are in a fire-proof but vented container (ammo boxes are good). I also never keep too many batteries together physically in the same container, as ifone goes obviously any adjacent will almost certainly ignite too.

Nigel R19/09/2018 15:22:56
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3099 forum posts
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Is there any good data on lifespan, for "fully charged" vs "storage" approaches?

If it's that bad, I might consider going back to all IC!

To best of my knowledge, in a fridge (in the garage!) at 30% full, is the ideal.

Former Member19/09/2018 16:00:19
1322 forum posts

[This posting has been removed]

The Wright Stuff19/09/2018 16:05:05
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1381 forum posts
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I really don't believe it's particularly sensitive. Anywhere between 20% and 50% isn't going to make any measurable difference to lifespan unless you study a dataset of thousands of batteries. As Matty says, the only real rule is not to store them fully charged.

I'm not aware of any good data on lifespan. It would take 2-3 years to collate such data, and since the battery technology will have evolved in that time, it would then be 2-3 years out of date.

Nigel R19/09/2018 16:06:40
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david, transport regs are "under 30%"

Biggles' Elder Brother - Moderator19/09/2018 16:28:58
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Posted by Nigel R on 19/09/2018 15:22:56:

Is there any good data on lifespan, for "fully charged" vs "storage" approaches?

If it's that bad, I might consider going back to all IC!

To best of my knowledge, in a fridge (in the garage!) at 30% full, is the ideal.

Best data Ican find is this sort of thing:from batteryuniversity.com

Storage Temperature  |      40% charged     |   100% charged
      0°C            |    2% after 1 year   |  6% after 1 year
     25°C            |    4% after 1 year   | 20% after 1 year
     40°C            |   15% after 1 year   | 35% after 1 year
     60°C            |   25% after 1 year   | 40% after 3 months

As you can see the move up to to a temp of 25C makes a considerable different to the impact of charge state on capacity loss. But the reality is that there are many factors at play here not just chagrge state. For example you can put a battery away at 30% thinking it will be fine. But Lipos self discharge so it won't stay at 30% - it will run down and if it goes below 3v per cell its knackered! So there is an argument for storage charging nearer 50% than 20%?

BEB

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