Each autumn the same thing happens: the lawn tools are wiped down, the batteries are pulled out, and all of them are pushed into the garage to be frozen until April. The tools are fine with it, but the batteries aren't and so they get their revenge on you in the spring.
There are three rules concerning battery storage: store the packs at about half charge, not fully charged and not empty; keep them cool and dry, which as a rule means keeping them indoors rather than in the garage; and remove them from both the charger and the tool. That's all, and this approach saves the batteries every single winter.
This guide gives you a complete step-by-step account of how to store power tool batteries during the winter and for the long term, including the precise charge level needed, the temperatures that are important, the setup errors that can cause batteries to be damaged, a winter checklist which you can carry out in ten minutes, and how to reactivate a stored battery. Details about batteries in general can be found in our electric tool battery guide.
The charge level rule: half full, not full and not empty
The level that most brands agree upon is between 30 and 50 per cent charge. If your device has a fuel gauge, this is generally equivalent to two bars. There's no need to think about it – two bars is the simple rule.
What about making the cells fully charged? A cell which is fully charged and then left for months will age more quickly since the chemistry remains under stress at the higher end. As for why not make them completely empty, it's because lithium batteries self-discharge very slowly and one that drops to true zero while it's sitting can go below the level at which the charger will even recognize it.
The real straightforward point is that battery advice isn't something that applies to all situations. According to Black & Decker's own instructions for winter storage, its batteries should be stored with a full charge, which is the opposite of the usual advice. Since the manufacturer's recommendations actually differ in this case, the deciding factor is the manual that comes with your battery. When you don't have a manual, two bars is the safe default.
If you still find the fuel gauge bars confusing, our article explaining what amp hours are will make the figures clear.
The temperature rule: cool beats cold
Lithium batteries perform just as well as you do in terms of weather conditions, with a general range of 40 to 80 degrees Fahrenheit; Ryobi's stated storage range is narrower, going from 41 to 68 degrees. The takeaway from both situations is that room temperature is best, freezing is bad, and heat is the worst.
| Guidance | Range |
|---|---|
| General rule | 40 to 80 degrees Fahrenheit |
| Ryobi's published storage range | 41 to 68 degrees Fahrenheit |
| Your parked car | All of the above, violated daily |
A parked car is the most undesirable place for storage since it experiences both the cold of winter and the heat of summer; likewise, an uninsulated garage is unsuitable for storage, which is the reason why the usual recommendation—though it actually works—is so odd: it is better to keep the tools in the garage and to bring the batteries inside. A shelf in a closet, a utility room, or a basement will do. The packs are small and the house doesn't mind.
The setup rules: off the charger, dry, covered
Here are three small things which do the job.
Not connected to the charger. If a pack stays on a charger for months it will be constantly charged and warmed, which is not proper storage.
Dry; since moisture and electronics don't get along there should be no damp corners in the basement and no wet spots under the pipes.
Protect the terminals by keeping the contacts clear of any loose metal, screws, keys, or other objects which could cause a bridge and result in the battery being short-circuited. It costs nothing to cover the terminals with a piece of tape, and the Power Tool Institute's advice on storage lists cool, dry conditions and keeping the battery away from flammable materials as its top priorities.
The winter checklist
Ten minutes in the fall beats a dead pack in the spring. Run this once per battery:
- Charge or discharge to about half. Two bars on the gauge.
- Take the pack off the tool and the charger.
- Bring it indoors. Closet, utility room, basement. Not the garage, not the car.
- Set it somewhere dry, away from metal and flammables. Tape the terminals if you want the extra margin.
- Put a calendar reminder six months out. Lithium self-discharges roughly 1 to 2 percent a month, so a six-month top-up keeps packs inside the safe zone.
If you want the bigger picture on why these habits matter, the lifespan numbers are in how long power tool batteries last.
Waking a stored pack back up
When spring arrives, the pack takes out of the closet and there are two things first.
Charge the pack only after it has reached room temperature since it will charge poorly and wear out more quickly if it is cold, and a pack taken directly from a freezing shelf should not be charged at all.
Then check it. If it's been sitting six months or more, the voltage may have drifted low, and that's normal up to a point. If the pack won't charge after warming up, our power tool battery not charging guide has the seven fixes, and if it's done for good, you can browse replacement batteries by brand across the twelve platforms we stock.
Common questions about battery storage
What charge level should batteries be stored at?
About 30 to 50 percent, which usually shows as two bars on the fuel gauge. Fully charged and fully empty both age cells faster, and fully empty risks dropping below the charger's detection voltage.
Should I leave batteries on the charger?
No. A charger keeps topping up and warming the pack, which is the opposite of storage. Take the pack off the charger once it's at your storage charge level.
Can I store batteries in the garage?
Not ideally. Uninsulated garages swing from freezing to hot, both of which age lithium cells. The better move is to leave the tools in the garage and bring the batteries indoors to a cool, dry spot.
How do you store power tool batteries for winter?
Charge or discharge each pack to about half, take it off the tool and charger, bring it indoors to a cool dry spot, and set a reminder to top it up in about six months. Ten minutes per pack in the fall.
Do batteries lose charge in storage?
Yes, slowly. Lithium packs self-discharge roughly 1 to 2 percent a month. That's why the storage charge starts at half and the six-month top-up exists.
It's boring to store batteries properly, and that's the idea. You should store them at half charge, in a cool and dry place, off the charger, indoors, and set a calendar reminder for six months ahead. In the fall spend five minutes on each pack and then in the spring the batteries will work at full capacity rather than requiring a trip to the shop.
References & Sources
- Ryobi support (battery storage temperature and charge level guidance)
- Black & Decker support (winter storage guidance)
- Power Tool Institute battery safety guidance (Power Tool Institute, the power tool industry's safety association)
Need a replacement?
If the pack in question doesn't survive the winter, you can browse for replacement batteries by brand. We carry compatible packs for twelve platforms and if you have any questions you can ask a real person via our contact page.