Should you store a battery full or empty?

Short answer: neither. If a lithium-ion battery is going to sit for weeks or months, store it at around half charge, somewhere cool. That covers your phone, laptop, cordless tool packs, drone, e-bike and power bank.

The two extremes fail in different ways. A full battery wears out slowly. An empty battery can fail all at once.

Battery	Store it at	Where
Phone, tablet, laptop	About 50%, switched off	Room temperature
Cordless tool packs	About half	Indoors, off the charger
E-bike, scooter, drone, power bank	About half	Cool and dry, not freezing
AA, AAA, 9V, coin cells	As sold (full)	In the packaging, room temperature

For weeks or months of storage. Your device maker's advice comes first.

What happens to a battery stored at 100%

Every lithium-ion cell ages just by existing, even on a shelf. Engineers call this calendar ageing. The main cause is a thin layer on the graphite electrode, the solid electrolyte interphase. It keeps growing slowly, and every bit of growth locks away lithium that can no longer carry charge.

How fast it grows depends mostly on two things: state of charge and temperature. A full cell has its graphite packed with lithium, which pushes the electrode to a low potential where that side reaction runs faster. A 2016 study from TU Munich stored cells at 16 charge levels from 0 to 100% and found that this low anode potential was the main driver of capacity loss in storage. Interestingly, the loss didn’t rise smoothly with charge. It came in steps, with wide bands of 20 to 30% of charge ageing about the same. A 2021 study from KIT found the same overall picture: storing at 100% had a large effect, while anything below about 80% made little difference.

Heat makes all of it worse. Battery University’s estimate for lithium-ion (lithium-cobalt) cells after a year of storage:

Storage temperature	Stored at 40%	Stored at 100%
0 °C	98%	94%
25 °C	96%	80%
40 °C	85%	65%
60 °C	75%	60% after 3 months

Capacity left after storage. Estimates for one older chemistry; newer cells do better, but the pattern holds.

At room temperature, a year at full charge cost five times more capacity than a year at 40% in that estimate. A full pack in a hot car or a summer garage is about the worst case.

The damage is permanent, but it’s gradual. A battery stored full still works afterwards. It just holds less.

What happens to a battery stored at 0%

An empty battery isn’t sitting still. It loses charge on its own (self-discharge), and most packs have a protection circuit that draws a little current too. Your phone or tool also switches off before the cell is truly empty, so “0%” leaves a small reserve. Months in a drawer use up that reserve.

Then two things happen as the voltage keeps falling:

1. The pack goes to sleep. Around 2.5 V per cell, the protection circuit cuts the pack off to protect it. A normal charger may then refuse to charge it, and it looks dead.
2. The cell gets damaged. Below about 2 V per cell, copper from the negative electrode starts to dissolve into the electrolyte. When the cell is charged again, that copper can come back as tiny metal bridges inside the cell, which raise self-discharge or cause a short.

Battery University’s advice is to discard a lithium-ion cell that has spent more than a week below 2 V. Apple puts it plainly: a device stored fully discharged “could fall into a deep discharge state, which renders it incapable of holding a charge.”

So full is a slow leak, and empty is a cliff. For a few weeks, a full battery loses a little capacity. For a few months, an empty one can be lost for good.

How to store a battery for months

1. Charge it to about half. Apple says around 50%. Battery University says about 40%, and adds that the exact number matters less than not being full.
2. Keep it cool and dry. Battery University recommends 15 °C. Apple says below 32 °C. A shelf indoors beats a hot garage or a car. Don’t freeze it.
3. Check it every few months. If it has dropped low, top it back up to about half.
4. Charge tool packs for the job, not for the shelf. Charging the day before is better than leaving packs full all season.
5. Leave a pack alone if it’s swollen or hot. A cell that has been deeply discharged for a long time isn’t worth forcing. Take it to a battery recycling point.

What about AA, 9V and coin cells?

Everything above is about rechargeable lithium-ion. Single-use batteries work differently: alkaline and lithium cells like AA, 9V and CR2032 are sold full and meant to sit that way. Storing them well is mostly about keeping them out of trouble:

• Keep them in the packaging until you need them. Loose cells rolling around a drawer touch each other, keys and coins. A 9V’s terminals sit side by side and short easily.
• Keep coin cells away from children. A swallowed coin cell can burn through the throat within hours, so treat it as an emergency.
• Take them out of devices you won’t use for months, like a camping lantern or the Christmas lights. An alkaline cell left in a dead device can leak and ruin the contacts.
• Room temperature is fine. They don’t need the fridge.

Not sure which battery a device takes, or whether the 357 in the shop is the same as your LR44? The battery equivalents chart lists every name each cell is sold under.

Where Battery Inventory fits

Cordless tool packs are the batteries most likely to sit for weeks between jobs, either left on the charger or forgotten flat. That’s why I built pack care into Battery Inventory. It keeps track of each pack’s charge and nudges you before one sits full or empty for too long, with a reminder to store it at about half.

For the rest of the house, it counts the AA, 9V and coin cells in your drawer, tells you which battery each device takes, and reminds you when one is due, so the spare is there before you need it.

Sources

• Keil, P. et al. (2016). Calendar Aging of Lithium-Ion Batteries: I. Impact of the Graphite Anode on Capacity Fade. Journal of the Electrochemical Society, 163(9), A1872–A1880.
• Werner, D., Paarmann, S. and Wetzel, T. (2021). Calendar Aging of Li-Ion Cells: Experimental Investigation and Empirical Correlation. Karlsruhe Institute of Technology.
• Battery University. BU-702: How to Store Batteries.
• Battery University. BU-410: Charging at High and Low Temperatures.
• Apple. Maximizing Battery Life and Lifespan.