The single most important thing you can do when storing a lithium-ion battery is charge it to about 40 to 50 percent and keep it in a cool, dry place. A battery stored this way at room temperature retains roughly 96 percent of its capacity after a full year. Store it fully charged at the same temperature, and you’ll lose significantly more. The details below will help you get the most life out of every battery you own, whether it’s a spare power tool pack, a laptop you’re shelving for the season, or a drawer full of portable chargers.
Why 40 to 50 Percent Charge Matters
Lithium-ion cells degrade faster when they sit at high voltage. A fully charged cell sits at about 4.2 volts, and at that level, a thin layer on the electrode (called the SEI layer) grows more aggressively, permanently consuming lithium that would otherwise contribute to capacity. Dropping the charge to 40 percent brings the cell voltage down to around 3.82 volts, which dramatically slows that degradation.
The good news: you don’t need to be precise. Hitting exactly 40 percent isn’t critical. Anywhere in the 40 to 60 percent range works well. Most devices and battery chargers display a percentage, so just unplug when you’re in that window. If your device only shows a vague bar indicator, pulling it off the charger around the halfway mark is close enough.
What you absolutely want to avoid is storing a battery that’s completely dead. When a lithium-ion cell drops below about 2.7 volts, unwanted chemical reactions permanently raise its internal resistance and reduce its capacity. Many batteries have a built-in protection circuit that cuts off power before voltage gets that low, but if a battery sits unused for years, slow self-discharge can eventually drag it past that threshold. At that point, the battery may never charge properly again.
Temperature Is the Other Half of the Equation
Heat accelerates every form of battery degradation. The safe storage range for lithium-ion batteries is roughly 20°F to 95°F, but the sweet spot is a cool room, somewhere around 60 to 70°F. At 77°F with a full charge, a lithium-ion cell can self-discharge about 20 percent per month. Drop the charge to 40 to 60 percent and the monthly loss falls to around 4 percent. At freezing (32°F), that same partially charged cell loses only about 2 percent per month.
A climate-controlled closet, basement shelf, or interior cabinet works for most people. Garages and sheds are risky because temperatures swing with the seasons. A garage that hits 110°F in summer will age your batteries far faster than indoor storage. On the cold side, batteries stored below about 50°F won’t be damaged, but their performance will be temporarily reduced until they warm back up. Just avoid charging a lithium-ion battery when it’s below 32°F, as that can cause permanent internal damage.
Remove Batteries From Devices
If you’re putting a gadget in a closet for months, pull the battery out when possible. Even when a device is powered off, its circuitry draws a small parasitic current that slowly drains the battery. The battery’s own protection circuit adds roughly 3 percent per month of drain on top of the cell’s natural 1 to 2 percent self-discharge. A device’s standby electronics can add even more. Over six months to a year, that trickle can pull the battery down to dangerously low voltage levels.
For laptops, phones, and other devices with non-removable batteries, power the device completely off rather than leaving it in sleep mode. Some laptops have a “shipping mode” or storage setting in the BIOS that disconnects the battery from the motherboard electronics. If your device offers that, use it.
Check and Top Off Every Six Months
Lithium-ion batteries can hold a partial charge for up to four years before fully depleting, but that doesn’t mean you should ignore them. Every six months, check the charge level and bring it back up to around 50 percent if it has drifted significantly. This simple habit prevents the battery from slowly draining into the danger zone below 2.7 volts per cell, where permanent damage begins.
If you check a stored battery and it won’t accept a charge at all, or the charger immediately shows “full” and then the battery dies within minutes, the cell has likely degraded beyond recovery. At that point, recycle it through a battery drop-off program rather than trying to force-charge it.
Physical Storage and Safety
Lithium-ion batteries are generally stable when treated properly, but thermal runaway (a rapid, self-sustaining increase in temperature) is a real risk with damaged or defective cells. Warning signs include the battery feeling unusually warm, visible swelling or puffiness in the casing, hissing or venting gas, and any unusual smell. A swollen battery should never be charged or used. Handle it carefully and take it to a battery recycling location.
For everyday storage, keep batteries away from metal objects like coins, keys, or loose screws that could bridge the terminals and cause a short circuit. Placing individual batteries in their original packaging, a plastic case, or even a simple zip-lock bag prevents accidental contact. Store them on a non-flammable surface, away from direct sunlight and anything that generates heat.
If you store a large number of lithium-ion batteries, such as spare packs for drones, power tools, or RC vehicles, fire-rated lithium battery cabinets and containers are available. These are lined with fire-rated coatings, typically rated for two hours of containment, and include pressure relief vents and filters to manage toxic fumes in the event of a cell failure. For most households, a fireproof bag (often marketed as a “LiPo bag”) offers a simpler, lower-cost layer of protection for a few batteries.
Humidity and Moisture
Aim for a relative humidity around 50 percent. Excessive moisture promotes corrosion on the battery terminals and connector contacts, which increases resistance and can make the battery behave erratically when you put it back into service. If you live in a humid climate and store batteries in a basement, a small dehumidifier or silica gel packets near the storage area help keep conditions in range. Wipe the terminals with a dry cloth before reinstalling any battery that has been in storage for a long time.
Quick Reference for Long-Term Storage
- Charge level: 40 to 50 percent (anywhere in the 40 to 60 range is fine)
- Temperature: Cool room temperature, ideally 60 to 70°F; never above 95°F
- Humidity: Around 50 percent relative humidity
- Device removal: Take batteries out of devices, or fully power down devices with built-in batteries
- Maintenance: Check charge level and top off to 50 percent every six months
- Terminal protection: Keep batteries in cases or bags to prevent short circuits
- Danger threshold: Never let a cell drop below 2.7 volts; permanent damage occurs