long term storage

[RythmshiP]

I am in posession of two 48V 17aH Lithium Ion batteries. Both belong to kits of which I may not get around to until spring. What is the best way to store these. In the refrigerator or freezer and at full capacity or just like they are still in box from china?

 

[El_Steak]

Most important thing is to disconnect any BMS that might be there or else you might end up with a 0V puffy pack in the spring.

You also don't want to store it fully charged (I store mine at around 40% capacity) and in cool temperature (I keep mine in the garage at around 3-10C during the winter).

I don't know if sub-freezing temperature are good or bad.

 

[neptronix]

Charge it to 60%.
Disconnect the BMS.
Leave it at room temp as that's where lithium is happiest.

 

[dogman dan]

Disconnect it from the bms.

I don't know about cold storage, lipo stays at room temp mostly because my safest storage place is room temp. Pings stay in the garage, but they don't really get below 32 there.

Lastly, check on it monthly at least. You got some weird trickle short, or just a cell that strangely wants to discharge itself, you want to find out about it too soon, not too late. I'd check the voltages weekly at first, then monthly when you have proven that will be often enough.

 

[El_Steak]

Here's more info and data on the subject of storage:

http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

So most important is state of charge (they recommend 40%) and then low temps.

Good advise from dogman on periodically checking the individual cell voltage. I lost a cell that way last winter, just slowly discharged on its own and puffed. I hadn't noticed that self discharging cell during riding season, as it was paralleled with other healthy cells and recharged every day.

 

[Kin]

Batteryuniverse recommend 40%, but the hobbyking charger does storage at 3.85v, which might be more like 60%. *probably doesnt make much of a difference.

 

[El_Steak]

You're right, it probably doesn't make a big difference. The storage mode on the Hyperion 1420i will give me anything from 3.7 to 3.9

 

[RythmshiP]

Thanks much for all the advice, will diconnect the bms at once and see if I can find a way to gauge what percentage the battery is as I do not posses a system monitor for these

 

[neptronix]

I say 60% because it will gradually drop capacity over a period of months and prolly end up at ~40% by the end of winter..

Drain the sucker down to cut off point.
Charge it & measure how many hours it takes to charge.
Then drain it down to 0% again..

Find out what 60% of that is based on how long it takes to charge.

that's the best you can do, if you don't have a turnigy watt meter, cycle analyst, etc to measure the amp hours..

 

[Drunkskunk]

I store mine around 3.8V, which is about 40% of usable capacity. I usually store them in the garage through the winter because the temp stays in the low 40s out there. Fridge or freezer would be better, but its good enough.

The voltage on a Lithium battery shouldn't drop off much. 2% percent a month when stored cold would worry me as excessively high.

El_steak's link has a good chart of storage temps. Lithium like to be stored cold, it slows down the chemical reactions that cause them to eventually degrade regardless of cycles.