You are about to shelve an old iPhone, a backup laptop, or a power bank you only grab for trips. The instinct is to charge it to 100% so it is “ready” whenever you need it. That instinct is exactly wrong. A lithium-ion battery sitting at full charge for months quietly loses capacity, and one left at 0% can drop so low it never wakes up again.
The fix is simple, and it is the same for phones, laptops, and power banks, because they all run on the same lithium-ion chemistry. Get the charge into a comfortable middle zone, keep it somewhere cool, and give it a quick top-up a couple of times a year. Here is exactly what that looks like.
Store any lithium-ion device at roughly 40-60% charge (Apple says aim for about 50%). Avoid leaving it at 100%, which speeds capacity loss, or near 0%, which risks a deep discharge that can disable the cell. Keep it powered off in a cool, dry spot, and top it back up to around 50% every six months or so.
The sweet spot is 40-60%, and 50% is a safe default
Battery makers and independent references converge on a partial state of charge for storage. Battery University recommends storing lithium-ion at roughly 40% (about 3.82 volts per cell) and notes that finding the exact level is not critical. Apple tells you to charge a device to around 50% before long-term storage. Laptop makers land in the same band: Lenovo’s Vantage software has a Conservation Mode that holds charge near 55-60%, and Dell Power Manager lets you cap charging well below full.
If you only remember one number, make it 50%. It sits comfortably inside every manufacturer’s recommended range, leaves headroom for slow self-discharge, and is easy to eyeball on a battery readout. You do not need to hit it to the percent.
Why 100% is bad and 0% is worse
A lithium-ion cell ages faster the longer it sits at a high voltage. The numbers are stark. Battery University’s storage data shows a typical Li-cobalt cell kept at 25 degrees C retains about 96% of its capacity after a year when stored at 40% charge, but only around 80% when stored full. That gap is permanent, lost capacity, not a temporary dip you recharge away.
The opposite extreme is more dangerous. A battery left near empty keeps self-discharging until the voltage collapses. Most cells include a protection circuit that shuts off around 2.5 volts, and a cell allowed to sit far below that for any length of time can suffer permanent internal damage, after which the device may refuse to ever charge it again. Apple warns that a fully discharged battery in storage “could fall into a deep discharge state, which renders it incapable of holding a charge.” That is the dead-power-bank-in-a-drawer scenario, and it is often unrecoverable.
Keep it cool, because heat is the real killer
Charge level matters, but temperature is the bigger lever. Heat accelerates the chemical reactions that age a battery, so a hot attic or a car glovebox in summer will degrade a stored cell far faster than the charge level alone. Battery University’s data shows that same cell at 40% charge dropping from 96% retention at 25 degrees C to about 85% at 40 degrees C over a year.
Aim for a cool, dry spot. Apple specifies storage below 90 degrees F (32 degrees C); Battery University points to around 15 degrees C (59 degrees F) as close to ideal. A closet, a drawer in an interior room, or a shelf away from radiators and windows all work. Cold is far less harmful than heat, but do not store devices below freezing or anywhere damp, and let a cold device warm to room temperature before you power it on.
Do this
Charge to about 50%, power the device fully off, and store it in a cool, dry, indoor spot. Add a calendar reminder to top it back up every six months.
Not that
Do not store it at 100% “to be safe,” do not let it run flat first, and do not leave it in a hot car, garage, or sunny windowsill.
The top-up schedule: every six months
Even switched off, a lithium-ion battery slowly self-discharges, typically a couple of percent per month at room temperature, faster if it is warm or stored near full. Over many months that adds up, and a device that started at 50% can drift toward the danger zone. The simple safeguard is a periodic check.
Apple’s guidance is concrete: if you store a device longer than six months, charge it back to 50% every six months. That cadence works as a universal rule. Set a recurring reminder, power the device on, bring it back to roughly half, then power it down and re-shelve it. For a phone, this is also a good moment to confirm it still boots; for a laptop, you can glance at battery health (here is how to check it on Windows 11).
Power banks and laptops: same rules, a couple of wrinkles
A power bank is just a lithium-ion cell in a case, so the 40-60% storage rule applies directly. The catch is that many power banks have no precise gauge, just a four-LED indicator, so “two of four lights” is your practical target. Top up on the same six-month rhythm so it never slips toward a deep discharge, which is the most common reason a long-forgotten power bank refuses to wake up.
Laptops add one option phones lack: if you must leave a laptop plugged in and running during a long idle stretch, enable the maker’s charge-limit feature (Lenovo Conservation Mode, Dell Power Manager, or the equivalent) so it hovers around 60% instead of pinning at 100%. For a truly shelved backup laptop, though, the cleanest move is the same as everything else here: about 50%, powered off, somewhere cool.
| Storage choice | What happens |
|---|---|
| Stored at ~40-60% | Best capacity retention; minimal aging during storage |
| Stored at 100% | Faster permanent capacity loss, especially if also warm |
| Stored near 0% | Risk of deep discharge that can disable the cell for good |
| Stored in heat (hot car, attic) | Accelerated aging regardless of charge level |
| Stored cool, ~50%, powered off | The recommended setup; top up to 50% every 6 months |
That is the whole playbook. Half charge, powered off, kept cool, and a quick refill twice a year. Do that and the phone, laptop, or power bank you put away will actually hold a useful charge when you pull it back out.
Frequently asked questions
What percentage should I charge a phone to before storing it for months?
Aim for about 50%, which sits in the middle of the 40-60% range that battery references recommend. Apple specifically advises charging a device to around 50% before long-term storage. You do not need to be exact; anywhere in the 40-60% band is fine.
Is it bad to store a power bank fully charged?
Yes, leaving a power bank at 100% for months speeds up permanent capacity loss, especially if it is also stored somewhere warm. Charge it to roughly half (about two of four LED lights on most models) before shelving it. Top it back up every six months so it does not slowly drain into a deep-discharge state.
What happens if a stored battery drops to 0%?
A lithium-ion cell left empty keeps self-discharging until its voltage falls very low. Most cells have a protection circuit that cuts off around 2.5 volts, and sitting far below that can cause permanent internal damage so the device refuses to charge again. This is why a power bank or phone left flat in a drawer for a year sometimes never powers back on.
Should I leave a stored laptop plugged in or unplugged?
For a laptop you are truly shelving, charge it to about 50%, power it fully off, and unplug it. If you must leave it plugged in and idle for a long time, enable the maker’s charge-limit feature (Lenovo Conservation Mode or Dell Power Manager) so it holds near 60% instead of staying at 100%.
How often should I top up a device that is in storage?
About every six months. Even powered off, lithium-ion batteries self-discharge a couple of percent per month, faster when warm, so a device that started at 50% can drift down over time. Apple recommends recharging back to 50% every six months for anything stored longer than that.