Best RC LiPo Battery Storage Practices.

by John Salt

From the RC LiPo battery page, we now know how a LiPo battery is made, how it works, the safety concerns, what to look for when purchasing one, how to charge and balance one, why over discharging is so harmful, internal resistance, what puffing is all about, and breaking in; what more can there be to cover?

RC LiPo Battery Storage!

I Store My Large LiPo's In Separate Metal Compartments For Safety. This Picture However Looked Kinda Neat When I Had Some Of Them Placed Together.

How you store your LiPo batteries between uses will greatly affect their lifespan and even how safe (stable) they are.

As I mentioned on the LiPo page, a LiPo cell that drops below 3 volts under load (about 3.5V open circuit voltage) is almost always & irreversibly damaged.

Puffed LiPo Cell Due To Improper Storage

It will have reduced capacity, puff up or not be able to accept a charge or deliver current after a charge due to cell oxidation and/or electrolyte gassing / decomposition.

Remember, a LiPo battery's life is always being nibbled away; damage is ongoing and accumulative.

The best we can do is ensure those nibbles are as small as possible. One place we can really minimize LiPo degradation without much effort is while our packs are sitting in storage. When you think about it, storage makes up most of a LiPo's life; less the precious time we are actually flying, driving or boating.

Best Storage Temperature & Voltage For LiPo Batteries

If your RC LiPo batteries are stored for any period of time in a discharged state, you risk irreversible LiPo damage.

What's a discharged state?

Most LiPo manufacturers will state 3.6 volts (open circuit voltage) is the absolute minimum a LiPo cell should ever be discharged down to (about 95% discharged). As we know from the LiPo page, a much heathier and safer maximum discharged cell voltage is 3.73V (about 80% discharged), especially in our high current sucking RC applications.

Regardless, as batteries sit, they will naturally self-discharge.

LiPo batteries are actually very good in this respect and self-discharge much slower than most other rechargeable battery types, but they still do lose voltage potential as they sit. If you leave them for a number of weeks or months in a near fully discharged state, chances are they'll be damaged.

You must store them charged, but not fully charged either; that will also damage them and cause electrolyte gassing.

Fully charged LiPo batteries are not happy and must be used soon after they are fully charged! I think of a fully charged LiPo pack as a pressure tank stuffed tight with angry electrons, just ready to burst!

I cover this fully charged topic in more detail on the LiPo Charging Page, but it's worth repeating.

You are likely okay to store a fully charged RC LiPo battery at or below room temperature for a day or two without doing too much damage. I personally follow as short a time frame as possible and only charge up my LiPo packs just before heading out to the flying field; meaning I never let packs sit fully charged overnight if at all possible.

LiPo Batteries, like Frosty the Snowman, don't like red thermometers.

Never store a LiPo in a hot environment (car or hot shed for example). That will certainly cause damage as I explained on the LiPo battery page, but it's worth repeating.

RC LiPo battery storage temperature is actually very important for improved LiPo life, some suggest even more so than storage voltage.

I personally store my LiPo packs in our cold storage room in the basement which never gets above 20C (68F) in the summer and is usually around 12C (54) in the winter.

For optimum LiPo battery life, store your RC LiPo batteries in a cool room if possible (10C to 15C / 50F to 60F) @ 40% to 80% relative humidity, at a 40% to 50% charged state.

A LiPo Cell @ 3.85V equates to about a 50% charged state.

This equates to LiPo storage voltage of around 3.80 to 3.85 volts per cell (open circuit resting voltage) as shown on this RC Battery Meter (such a useful tool in this hobby).

I've seen several LiPo battery manufacturers list storage state numbers as high as 30-80%; about 3.75V to 4.00V open circuit voltage. However, since most computerized RC chargers set the LiPo storage charge at 40% to 50% (3.80 to 3.85 volts per cell), and most good quality LiPo packs come from the factory around that voltage range as well, that's what I recommend and what I follow myself.

Computerized RC Charger Set To Storage Charge Program

RC Charger Set To LiPo Storage Program Where It Will End The Charge Cycle When All The Cells In This 6S LiPo Pack Reach About 3.85V.

RC LiPo Battery Storage Voltages Based On Cell Counts at a 40% to 50% Charged State:

6S LiPo @ 50% Storage / 23.1V

1S = 3.80 to 3.85 volts
2S = 7.60 to 7.70 volts
3S = 11.40 to 11.55 volts
4S = 15.20 to 15.40 volts
5S = 19.00 to 19.25 volts
6S = 22.80 to 23.10 volts
7S = 26.60 to 26.95 volts
8S = 30.40 to 30.80 volts
9S = 34.20 to 34.65 volts
10S = 38.00 to 38.50 volts
11S = 41.80 to 42.35 volts
12S = 45.60 to 46.20 volts

Everything about LiPo use and care is a compromise, and storage is no exception. The less energy stored in your LiPo packs (up to a point) while in storage, the safer they are but the charging times will be a little longer. Your call what's most important.

Personally, I like storage charging my LiPo packs to 50% capacity; only because the full charge cycle when I'm rushing to go flying is slightly shorter in time then if they were at a 40% charged state that many LiPo manufacturers will ship LiPo packs at for safety.

RC LiPo Storage Box & LiPo Storage Safety

As I mentioned at the top of this page, and on my RC LiPo Battery Page in the LiPo Safety section; I personally store all my LiPo's in a metal tool box/chest.

I also have a smoke detector in close proximity to my LiPo storage area and a fire extinguisher.

I also mention in that LiPo safety section other good low cost RC LiPo Battery storage ideas such as concrete blocks, repurposing old BBQ's, clay pots, low cost army surplus metal ammo boxes, or making your own LiPo storage containers / dividers out of cement board.

The options are only limited by your imagination and of course that your RC LiPo storage container will properly contain a flaming LiPo or a few LiPo's if they were ever to go all out napalm on you. In short, the container must be made from a material that doesn't burn while it contains rapidly oxidizing LiPo electrolyte goo!

It's very unlikely a LiPo will catch fire while in storage, but if you are the type of person where the only luck you have is bad, it's not 100% impossible.

Anecdotally, I've never had a LiPo erupt into napalm while in storage over the past 17 years. I have however had two separate occurrences where worn LiPo power leads accidently shorted together, but no fire; only a couple ballooned hot packs that vented and smoked. I'm of course very glad they were in a metal chest when it happened and not a wooden or plastic one.

You'll sleep better at night and while away from home knowing your LiPo's are in a fire safe container of some sort; at least I sure do.

If you don't want to build your own fire proof RC LiPo battery storage container or convince your better half you need a shiny new BBQ so you can use the old crappy one for your RC LiPo battery storage, there are many options you can purchase as well.

Of these, the compartmentalized square LiPo storage box types in my opinion are much better than the thin LiPo storage bags (for larger LiPo packs anyway), because most box type are made from a thicker fire proof material.

Here's just one example.

Stay LiPo Safe!