Workshop
Keeping Cordless Tool Batteries Out of Trouble
The battery packs on the grease gun, the impact wrench and the electric suction cup are lithium cells, and lithium cells have rules. Here is what OSHA and the U.S. Fire Administration say about charging, storing and retiring them, and what it looks like in a barn or a truck.
Four of the tools on this site run on lithium battery packs, and a fifth charges a lithium cell over USB-C. The grease gun kit and the impact wrench each ship with two 21 V 4.0 Ah packs, the electric suction cup with four 3.0 Ah packs, and the electric scissors with a built-in cell. That is a lot of stored energy living in the back of a truck or on a shelf in a barn, and the people who study battery fires have written down what to do about it. The rules are short.
What the two sources say
OSHA's Safety and Health Information Bulletin on small lithium battery devices and the U.S. Fire Administration's page on battery fire safety overlap almost entirely, which is a good sign that the advice is settled. Between them: remove batteries and devices from the charger once fully charged. Store packs in dry, cool places, away from anything that can burn, out of direct sunlight and out of hot cars. Charge above freezing and, in the Fire Administration's figures, between 32°F and 105°F, and keep every lithium battery below about 130°F. Buy replacement packs and chargers made and approved for the device by its maker or an authorized reseller. Stop using any battery that gives off an odor, changes color or shape, gets too hot, leaks or makes odd noises, put it in a fire-resistant container, and recycle it instead of throwing it in the trash.
| Rule | Where it comes from |
|---|---|
| Off the charger once full | OSHA bulletin |
| Charge between 32°F and 105°F | U.S. Fire Administration |
| Keep packs below about 130°F | OSHA bulletin |
| Store away from anything that burns, out of sun and hot cars | Both |
| Maker's packs and chargers only | OSHA bulletin |
| Odor, swelling, heat, leak or noise: out of service, fire-resistant container | Both |
| Recycle, never the trash | U.S. Fire Administration |
Charging: temperature and timing
The temperature rule is the one a working tool breaks most often. A pack that spent the night in a truck in January is below freezing when you bring it in, and charging it cold damages the cells in a way that does not show until later. Let it warm to room temperature first. The other end is just as real: a charger on a bench by a south window in July, or in a closed cab, runs the pack past the 105°F the Fire Administration names for charging. The charger belongs on a shelf in the shade, on something that does not burn, and the pack comes off it when the light says full. A full pack left on a charger overnight is the single habit both sources name first.
The impact wrench and the grease gun kit each come with two packs for a reason: one works while the other charges, which means the charger runs during the day, in sight, and not overnight. The electric suction cup's four packs each take one and a half to two hours to fill, so a rotation of four keeps a tile job going all day with the charger never unattended.
Storage: where the packs live
A grease gun lives near hay, diesel and shop rags, and an impact wrench lives in a truck that sits in the sun. Neither is where a lithium pack should spend the summer. The rule from both sources is a dry, cool place away from anything that can burn, and the practical version is a metal cabinet or an ammunition can on a concrete floor, with the packs out of the tools. Out of the tools matters: a pack in a tool in a bag can be switched on by whatever is packed on top of it, and a tool that runs in a closed bag gets hot.
Partial charge is fine for storage. A pack kept at full charge in heat ages faster than one kept half full, and a pack run flat and left flat for a season may not come back. Somewhere in the middle, in a cool cabinet, is where the packs you are not using this month should sit.
The signs of a pack that is done
The Fire Administration's list is the one to memorize: odor, a change in color or shape, too much heat, a leak or an odd noise. Swelling is the sign people see most on tool packs. A pack that no longer sits flat in the tool, or whose case has a bulge, has gas building inside it, and the next thing it can do is vent. Heat is the sign people feel: a pack that is hot to the touch after a charge, not warm, is a pack to set down somewhere non-flammable and leave alone. A smell like solvent is the sign people ignore, and it should not be ignored.
- Odor, especially sweet or solvent-like.
- A bulge in the case, or a pack that no longer seats in the tool.
- Heat after charging or in use that is more than warm.
- Any leak, any discoloration, any hiss or crackle.
A pack showing any of those goes out of service into a fire-resistant container, in the OSHA bulletin's words, and then to a battery recycler. Hardware stores and many municipal transfer stations take lithium packs. The trash truck does not, and a lithium pack crushed in a compactor is how a lot of truck fires start.
Replacements and chargers
Both sources say to buy replacement packs and chargers made and approved for the device, from its maker or an authorized reseller. The reason is that the charger and the pack are designed together, with the charger reading the pack's temperature and state and stopping when it should, and a charger that does not know the pack cannot do that. The Bluebow kits ship with their own charger in the case, and a second pack for the kit is the one that matches it.
The electric scissors are the exception on this site: they charge over a USB-C cable from any phone charger, and the cell inside is small. The same temperature rules apply, and the same sign of swelling, but the energy involved is a fraction of a tool pack.
Cold mornings and hot afternoons
The two temperatures that matter are the ones a tool meets on an ordinary day. Below freezing a lithium pack still delivers, with less runtime, and the harm is in charging it while it is cold, so a pack that spent the night in the truck warms indoors before it goes on the charger. Above the hundred-degree mark the risk flips: a pack on a dashboard, in a closed cab or on a charger in the sun runs past the figures both sources name, and heat is the condition that ages cells fastest and the one that comes before most failures.
The habit that covers both ends is the same. Packs ride in the cab, not the bed. They charge indoors, on a bench, in sight. They sit in a cabinet between jobs. No thermometer is needed: a pack that is too hot to hold comfortably is too hot to charge, and a pack that feels like a stone from the cold is not ready for the charger either.
A battery day in the barn
Here is what the rules look like on a day of greasing a tractor and its implements. The two packs come out of the cabinet in the morning, one onto the gun and one onto the charger on the bench in the shop, not in the cab. The gun runs its dozens of fittings on the first pack, which comes off warm but not hot. The packs swap at lunch. When the last fitting is done, both packs come off the gun and the charger and go back to the cabinet, half full or better, and the gun goes in its case wiped down. Nothing stays on the charger overnight and nothing stays in the truck. The grease gun guide and the farm set put the same habits next to the tools they belong to.
