Keep Milwaukee Batteries From Draining in Storage

Updated 5 November 2026 · Standard formula, shown below

This guide explains how to store Milwaukee M12 and M18 lithium-ion batteries so they hold their charge for months instead of draining to empty. You will learn the ideal charge level, temperature, and storage habits, plus what to do if a battery has already lost its charge.

What You’ll Need

Milwaukee battery charger (for checking and topping off charge)
Dry, cool storage area (garage shelf, closet, drawer)
Optional: voltage meter or Milwaukee battery gauge (if your battery lacks a built-in fuel gauge)
Optional: storage case or plastic container to keep batteries clean and dry

Step-by-Step

Charge to 30-50% before storage. Do not store a battery fully charged or completely empty. Use the charger to bring it to about 40% capacity. If your battery has a fuel gauge (the small button and LED lights), charge until the first LED lights up solid, which typically indicates around 25-50%.
Remove the battery from the tool. Even when the tool is off, it can draw a small parasitic current from the battery. Always detach the battery pack and store it separately.
Clean the contacts. Wipe the metal terminals on the battery with a dry cloth to remove dirt, dust, or corrosion. This prevents poor contact and reduces self-discharge.
Find a cool, dry place. The ideal storage temperature is between 40Â°F and 70Â°F (5Â°C to 21Â°C). Avoid attics, garages that get hot in summer, or sheds that freeze in winter. A shelf in a climate-controlled room or a basement closet works well.
Keep batteries away from metal objects. Do not store loose batteries in a drawer with coins, keys, or screws. These can short-circuit the terminals and cause rapid discharge or even a fire hazard. Use a plastic case or the original packaging.
Check the charge every 3-6 months. Lithium-ion batteries self-discharge slowly, but they will eventually drop below the safe threshold. Every few months, check the voltage or use the fuel gauge. If it’s below 20%, recharge to 40%.
Store batteries upright. While not critical, keeping them upright prevents any internal electrolyte from pooling and reduces stress on the casing.
If storing long-term (over a year), consider charging to 100% once a year. This helps rebalance the cells. Then discharge back to 40% before putting it back into storage.

Common Mistakes

Storing at 100% charge. A fully charged lithium-ion battery degrades faster and can lose capacity even when not in use. It also increases the risk of swelling.
Storing at 0% charge. A completely dead battery can drop below the minimum voltage, causing the internal protection circuit to shut off permanently. The battery may become unchargeable.
Leaving the battery on the tool. Even with the tool off, the battery is still connected to the tool’s electronics, which drains it slowly.
Storing in a hot garage. High temperatures accelerate chemical reactions inside the battery, increasing self-discharge and permanent capacity loss.
Storing in a freezer. Extremely cold temperatures can damage the battery’s internal structure and cause condensation that leads to corrosion.
Ignoring the fuel gauge. If your battery has a gauge, use it. Guessing the charge level often leads to overcharging or complete discharge.

Tips

Label your batteries. Write the purchase date or the last charge date on the battery with a marker. This helps you track which ones have been sitting for a while.
Rotate your batteries. Use the oldest batteries first. This prevents some batteries from sitting in storage for years while others get used daily.
Use a voltage meter. If you have a multimeter, you can check the exact voltage. A fully charged 18V battery reads about 20V; 12V battery reads about 12.6V. For storage, aim for around 15V on an 18V battery and 9V on a 12V battery.
Store in a fire-resistant container. While rare, lithium-ion batteries can fail. A metal toolbox or a LiPo-safe bag adds a layer of safety.
Keep the original packaging. The plastic clamshell or cardboard box protects the battery from short circuits and moisture.

Troubleshooting

Battery won’t charge after storage. If the battery has been sitting for months and won’t take a charge, it may have entered “sleep mode.” Try placing it on the charger and leaving it for 10-15 minutes. If the charger shows a red light, the battery is too low. Some Milwaukee chargers have a “boost” mode that can revive a deeply discharged battery. If that doesn’t work, the battery may be permanently damaged.

Battery drains faster than expected. If a stored battery loses charge quickly, it might have an internal short or be nearing the end of its life. Check the battery for swelling or damage. If it’s swollen, stop using it and dispose of it properly.

Battery gauge shows empty but the battery works. This can happen after a deep discharge. Charge the battery fully, then use it until it’s empty, then charge it again. This may recalibrate the gauge.

Battery is too cold to charge. If you stored it in a cold garage, bring it inside and let it warm to room temperature before charging. Charging a cold battery can damage it.

Battery won’t fit back on the tool. If the battery has swollen, it may not fit. This is a sign of internal damage. Do not force it. Replace the battery.

Frequently Asked Questions

Q: How long can I store a Milwaukee battery?
A: With proper storage (40% charge, cool dry place), a lithium-ion battery can last 1-2 years without significant capacity loss. You should check the charge every 6 months.

Q: Is it okay to store Milwaukee batteries on the charger?
A: No. Leaving a battery on the charger keeps it at 100% and can overheat it. Remove it once it’s charged.

Q: Can I store my batteries in a refrigerator?
A: Not recommended. The moisture and cold can cause condensation and damage. A cool, dry closet is better.

Q: What does the blinking light on the charger mean?
A: A blinking red light often indicates the battery is too hot or too cold. Let it reach room temperature and try again. A blinking green light may indicate a faulty battery.

Q: How do I know if my battery is dead for good?
A: If it doesn’t charge after several attempts, won’t hold a charge, or shows physical damage (swelling, cracks), it’s likely dead. Dispose of it at a recycling center.

Q: Does draining the battery completely before storage help?
A: No. For lithium-ion batteries, deep discharge is harmful. Always store at 30-50%.

Method: the standard formula for this calculation, rounded as each result states. See how the calculators work or report an error.