Storing a lithium-ion battery at full charge keeps its internal chemistry under higher voltage stress for longer, which speeds up the slow, permanent capacity loss that all these batteries experience over time. A pack left topped up on a shelf for months will typically hold less charge than one stored partly discharged.
Why does full charge stress a lithium-ion battery?
A lithium-ion cell sitting at full charge is at its highest internal voltage, and that’s the state in which the chemical reactions inside it are least stable. Held there for long stretches — not during use, but during storage — the electrode materials degrade a little faster than they would at a more relaxed, partial charge.
This isn’t a fault or a manufacturing defect. It’s a basic property of how lithium-ion cells work, and it affects the batteries in phones, laptops and cordless tools alike. The practical effect for a workshop is simple: a battery that spends most of its life fully charged and idle will age faster than one that spends most of its idle time at a lower charge.
For a fuller look at how these packs age in normal use — not just in storage — see how lithium-ion tool batteries actually age.
Does this mean batteries shouldn’t be charged before storage?
No — it means full charge is fine for using the tool, but not ideal as a long-term resting state. The distinction is between charging for a job and leaving a battery sitting at that same full charge for weeks or months afterwards with nothing to do.
Charge a battery fully when there’s a job to finish. If it’s coming off the charger and going straight back into a drawer for the season, that’s the situation worth avoiding — not the act of charging it in the first place.
What is the “ideal” storage charge level?
Manufacturers generally recommend storing a lithium-ion pack at a partial charge — noticeably below full but not run flat either — rather than at either extreme. The exact figure varies by manufacturer and by battery chemistry, so the tool’s own manual or the battery manufacturer’s documentation is the source to check, not a general rule of thumb.
In practice, many hobbyists manage this by simply not topping a battery back up to full the moment it comes off a job if it isn’t needed again soon, and by not letting a spare pack sit untouched at 100% for the whole off-season.
Does heat make it worse?
Yes. Heat and high charge together accelerate degradation more than either factor alone, so a fully charged battery stored somewhere warm ages faster than the same battery stored somewhere cool.
A battery left in a car boot in summer, on a sunlit windowsill, or on a shelf directly above a radiator is under more stress than one kept in a stable, moderate temperature. This is the same logic that governs where any tool should live — see what workshop humidity does to tools and timber for the parallel issue with damp and metal parts, and the wider habits in how tools should be stored to stop them rusting.
What actually happens if a battery is left flat instead?
Running a lithium-ion pack all the way down and then leaving it discharged for a long period is arguably worse than storing it full. Very low voltage for extended periods can push some cells into a state some manufacturers describe as “deep discharge,” from which the pack may not recover cleanly, or may recover with reduced capacity.
This is one reason cordless tool batteries generally shouldn’t be left in a fully drained state for months at a time any more than they should be left permanently topped up. Somewhere in between, and checked periodically, is the safer long-term habit.
How should batteries be stored between projects?
A few habits address most of the risk without requiring any special equipment:
- Avoid leaving a battery at full charge for weeks when it isn’t about to be used.
- Avoid letting a battery sit fully drained for an extended period either.
- Keep batteries somewhere cool and dry, away from direct sun, radiators or a hot car.
- Check on batteries that are stored for a whole season and give them a top-up charge if they’ve drifted very low, following the manufacturer’s guidance for that model.
- Keep packs off bare concrete floors and away from metal shelving that can hold cold and damp, similar to the advice covered in what a shadow board actually improves for organising a small workshop.
None of this requires buying anything extra — it’s a matter of habit rather than kit, which is why it sits comfortably alongside general good practice in tool care and maintenance.
What about batteries left in the tool itself?
Leaving a battery clipped into a drill or driver that then sits untouched for months has the same storage effect as leaving it on a shelf, plus it keeps the battery in contact with the tool’s own electronics, which is not usually a problem but adds no benefit either.
For a tool that’s genuinely in regular rotation, this doesn’t matter much — the battery is cycling through charge levels anyway. It’s the tools and spare packs that get put away for an off-season, a house move, or a long gap between projects where the storage charge level starts to matter.
When does this actually matter, and when doesn’t it?
It matters most for spare batteries, seasonal tools, and packs that get bought in twos and threes and then not all used evenly. A single battery in daily use for a current project is going through its own charge-and-discharge cycle regularly, and storage charge level is a minor factor next to how it’s actually being used.
It matters least for anyone who charges a battery, uses it, and recharges it again within a normal working week. The concern is really about idle time at extremes — full or empty — stretching into weeks and months, not the everyday business of charging a tool before a job.
Understanding what drives a spec like this is also useful when comparing cordless tools in the first place — see what volts and amp-hours actually tell you about a cordless tool and what brushless means for a power tool motor for related buying questions. For broader guidance on comparing tools before a purchase, the buying tools guide hub and the power tools archive cover the wider ground, and general storage habits for the rest of the workshop are gathered in workshop and storage.
Find Tool publishes general information, not professional advice. Power tools, mains electricity and workshop machinery are genuinely dangerous, and the safe settings, guards and procedures differ between models — always follow the manual and the markings on the tool in front of you rather than a general guide. Never remove or defeat a guard or safety feature. Anything involving fixed wiring, gas or structural work belongs to a qualified tradesperson. Wear the eye, ear and respiratory protection the task calls for.
Featured image: Photo by Rosser1954, source, CC BY 4.0