storage of batteries

[Valet]

What is the best way to store a li-po battery for over 3 months??? thanks

 

[AlanN]

Charge to about 60% capacity.

When needed charge up and balance.

 

[JfromJAGs]

http://www.batteryuniversity.com/parttwo-34.htm

Base on the above I recommend to store them cold and with only 20-40% capacity. Before use, bring them to room temperature and discharge them at 1C to 3.3V. Then charge them normally. Warm them externally before usage.

Joerg

 

[Flying Scotsman]

http://www.batteryuniversity.com/parttwo-34.htm
Base on the above I recommend to store them cold and with only 20-40% capacity. Before use, bring them to room temperature and discharge them at 1C to 3.3V. Then charge them normally. Warm them externally before usage.

Joerg

Joerg, An interesting reply...what temperature for storing?

Douggie

 

[jayt]

An interesting perspective, but I wonder how well it applies to how we use our cells. Ours do not have "fuel gauges" or "protection circuits", nor do they run for 2-3 hours before recharging. Based on Figure #1 there is only a negligible (2%) difference in life between storage at 0C and 25C - I can't see the justification for storing in a refrigerator versus in a cool house. But storage at a 40% charge level clearly can impact cell life dramatically. I am guessing that 40% charge would be between 3.6 and 3.7 resting volts?

Just thinking out loud, thanks for the link Joerg!

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[JfromJAGs]

The link I posted was basically aiming at LiIon laptop batteries - but these are Li based as well and basically a very similar chemistry to what is use in LiPo cells. Anyway, it makes sence that ageing of any chemical battery is higher the higher the temperatures are. Second, it is well known that Li based cells (LiIon and LiPo) loose capacity quicker when stored fully charged.

The longest test I have done is 1/2 year with a 5000 mAh TP cell: I stored it in a cold room (about 10-12°C) at 3.2V/cell. No measurable capacity loss. But as the manufacturers deliver the cells at 3.8V my recommendation is somewhere inbetween. 3.5-3.7V seams to be a good voltage. Also as general storage voltage inbetween races, but only when cells are stored cold and self discharge is rather low. I have not tested the difference between a cold room and a fridge. But a little above freezing seams a good temperature for storing to me. But as the IR is rather high when that cold, I strongly recommend to warm them before discharging them again. I would also remove the storage charge slowly before using them at high rates.

Loosing another 2% capacity may seam low, but you loose 2% at 0°C and 4% at 25°C. So this is 100% higher loss. A question of perspective...

Joerg

 

[Flying Scotsman]

This is a very interesting subject. I have stored my TP Extreme LI-PO cells at a 50% charge level and at room temperature in the basement...60 F (15C) to 80F (25C) and have found that capacity has dropped over 2 years by about 10% per annum. The useage is sport boating about 6 runs per year per battery and no silly hot setups e.g. DF 29.5 4S1P 4500 22.5C X440 9XL Turnigy 100HV. All temperatures were well within reason after running and initial temperature of 90 F. I use a Cellpro charger. In fact one battery lost it's capacity to recharge and balance properly with no useage apart from periodic (4 months) charging and discharging to 3.6v and then charging to 50%. I have 4 sets of TP 4500 3S1P and 2S1P and I run in series. Any suggestions?

Douggie

 

[jayt]

First - how did you measure your capacity change? Second - the cell autodischarge you reported sounds suspicious, especially since the pack assemblers store their assembled packs at 3.8 volts and they do not do what yours did after even longer storage times. That sounds more like defective cells than an operator storage problem to me.

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[Flying Scotsman]

Jay, I use a Micropower logger. The auto discharge unit is an ICE charger set at the max...arround 8 amps for LI-PO and a 3.6v cut off

Douggie

 

[Ron D]

From personal experience with my 4S LiPo's and having read the same article, I agree with what Joerg has passed on. What seems more to be the issue is the mechanics of accomplishing all that, so here is what I do: When I get back from a race I simply leave the batteries in whatever state of charge the came out of the boat at which is typically about 50%. I also put a blinkie on them to balance them at their lower state of charge. That is good enough for short term (2-3 weeks) storage between events. For anything longer than that (e.g. long term storage), I discharge them using my AstroFlight 109 charger and a Blinkie and then charge them on my FMA Direct CellPro 4S charger using the 50% storage charge mode. That done, I put them in a freezer bag with some dessecant packages and put the lot in the refrigerator (34-40 degrees F). When it is time to use them again, they come out of the refrigerator and go to the shop for a day or two to stabalize at room temperature. Next step is to discharge on using the AstroFlight 109 and Blinkie which warms them up a bit and then recharge using the CellPro on 1C Auto mode. I am now finishing a second season on four of my packs and they all charge up to 96-98% currently. I expect I can get another year or so off of them. The new ones I started the year with have not lost a step (yet). The three oldest packs are 3700 mAh 25C rated, the next oldest are 4000 mAh 20C rated and the three newest 4500 mAh packs are 30C rated.

When I am competing, I typically use the AstroFlight Charger and Blinkie and charge at 0.9C. I find that this is faster than the CellPro charger but only brings the cells up to about a 90-95% level but balanced. The CellPro can finish the job if time permits.

 

[jayt]

Jay, I use a Micropower logger. The auto discharge unit is an ICE charger set at the max...arround 8 amps for LI-PO and a 3.6v cut off

I am not very familiar with that equipment. IMO the "best" way to measure pack capacity is to obtain a baseline when the packs are near new. Charge the pack on one particular charger at one particular setting (write it down). Discharge the pack with one particular discharger (not in a boat) to the same voltage setting, then recharge at a particular rate (write it all down). This identifes the "true" pack capacity relative to that test equipment. Repeat this same test periodically (as close to the same as possible) to track changes in capacity. To do this any other way is just not good science - too many variables.

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