If you've got a pile of cordless tool batteries sitting in your garage or truck, you're sitting on a safety hazard waiting to go wrong. Lithium-ion batteries don't fail often, but when they do — overheating, swelling, even catching fire — it's almost always because of how they were stored. I've been a job-site electrician for over a decade, and I've seen perfectly good batteries killed by nothing more than bad storage habits. The good news? Proper storage is dead simple once you know the rules.
This guide walks you through exactly how to store your power tool batteries the right way — temperature, charge level, containers, and the mistakes I see guys make every single day.
What You'll Need
Before we get into the steps, grab these basics:
- A cool, dry storage location — not your truck bed in July, not the shed in January
- A non-conductive container — plastic ammo box, silicone battery case, or a dedicated fireproof bag
- A voltmeter or multimeter — for checking charge levels if you're not sure
- Labeling tape or a marker — for dating batteries before long-term storage
- A fireproof bag (optional but recommended if storing indoors)
Step 1 – Know the Right Storage Temperature
Lithium-ion cells are happiest between 50°F and 77°F (10°C – 25°C). Anything outside that range starts stressing the chemistry.
⚠️ Common mistake: Leaving batteries in a car during summer. I've pulled batteries out of work trucks in August that were too hot to hold. A lithium pack sitting in 120°F+ cabin heat degrades fast — internal resistance climbs, capacity drops permanently. Same problem in winter: Below freezing, the electrolyte thickens, and charging a cold battery can cause lithium plating on the anode, which is a one-way ticket to failure or fire.
If you have a heated garage, that's ideal. If not, bring batteries inside during extreme weather — a closet shelf works fine.
Step 2 – Charge to the Right Level Before Storage
This is the rule that trips up most people. Do not store your batteries at 100% charge, and do not store them dead flat.
The sweet spot: 40% – 60% charge.
At 100%, the internal voltage is maxed out, which accelerates electrolyte breakdown and increases the risk of swelling or venting. At 0%, the battery management system (BMS) can drain the cells below the safe cutoff voltage — that's how you get a battery that never charges again.
If you've got a charger with a storage mode, use it. Otherwise, run the battery down to about two bars, or check it with a multimeter (roughly 18V – 19V for an 18V pack, 20V – 21V for a 20V Max pack).
Need to top up your battery fleet? Check out our selection of Dewalt 20V replacement batteries if any of your old packs aren't holding a charge anymore.
Step 3 – Clean the Terminals and Inspect the Housing
Before putting batteries away, give them a once-over. Dirt, dust, and metal shavings on the terminals can create a slow short or corrosion over time.
- Wipe the contact rails with a dry cloth or a cotton swab dipped in isopropyl alcohol
- Look for cracks in the plastic housing — a cracked case can let moisture in
- Check for swelling. If the battery case is bulging, do not store it. Dispose of it properly at a battery recycling center
⚠️ Risk alert: Never try to puncture or "burp" a swollen battery. It's under internal pressure and can rupture violently. Bag it in a non-conductive container and take it to a hazardous waste drop-off.
Step 4 – Store in a Safe Container Away from Combustibles
Don't just toss batteries loose into a toolbag or drawer where metal tools can short the contacts. The terminals on lithium packs carry enough current to melt a screwdriver tip.
Good options:
- Plastic ammo box — cheap, stackable, non-conductive
- Silicone battery storage case — soft, prevents rattling
- Fireproof LiPo bag — limits oxygen in the unlikely event of a thermal runaway
- Original manufacturer case — fine as long as terminals are covered
Keep the storage container away from paper, rags, gas cans, or anything flammable. In a workshop, put it on a concrete floor or a metal shelf, not on a wooden bench.
For more detailed tips on charging routines and shelf-life management, read our power tool battery maintenance tips guide.
Common Mistakes to Avoid
Here's what I see most often on jobsites and in home workshops:
- Storing on the charger. Leaving a battery on the charger 24/7 keeps it at 100% and cooks the cells. Always pull it off once fully charged.
- Mixing dead and charged batteries in the same drawer. The charged pack can slowly discharge into the dead one through the terminals if they touch.
- Storing in direct sunlight. Even through a window, UV and heat accelerate degradation.
- Ignoring the "use it or lose it" rule. If you're rotating batteries, cycle them through a full discharge/charge at least every 3 months. Lithium cells deteriorate faster when they sit unused for long periods.
Frequently Asked Questions
Can I store lithium batteries in a freezer?
No. Freezer temperatures can cause condensation inside the battery and damage the electronics. Stick to 50°F – 77°F.
How long can you store a lithium battery without using it?
At 40%–60% charge in proper conditions, 6–12 months. After that, you'll want to recharge it to the storage level to avoid deep discharge damage.
Is it safe to store batteries in a plastic bag?
Only if you cover the terminals. A plastic bag alone doesn't prevent terminal contact with metal objects. Use a proper container.
What do I do if a battery starts swelling during storage?
Remove it from the storage area immediately. Place it in a fireproof bag or a metal container with a loose lid, away from anything flammable. Take it to a battery recycling location.
Can I store different brands together in one box?
Yes, as long as the terminals don't touch each other. Keep batteries upright or with terminals covered, and they'll be fine sharing a container.
That covers it. Follow these steps and your lithium-ion packs will last years longer — and you won't have to worry about waking up to a fire in the workshop.