Why will my tool battery not charge, and what do the charger lights mean?
Reading the charger before assuming the pack is dead — temperature hold-off, a dead charger, dirty terminals and the one failure that is genuinely permanent.
- Difficulty
- beginner
- Time
- 15 min
- Read
- 4 min
- Safety
- warning
Short answer
Work down the chart: no light at all means the charger or the socket, a steady non-charging light usually means the pack is too hot or too cold, and a rapid flashing fault light means testing a second pack to see whether the fault is in the pack or the charger. A pack stored flat for months has often gone below the point where it can be recovered.
Charger lights are one of the least standardised things in the tool world, and the manual is invariably lost, but the underlying states are common to nearly all of them: nothing, ready, charging, complete, waiting on temperature, and fault. Working out which state you are looking at answers most of the question. The flowchart follows the diagnosis in order.
Safety
Step by step
- Look at the pack before anything else.Swelling, splits, heat when idle, an odd smell, corrosion on the terminals. Any of those and the diagnosis stops — it goes to recycling and does not go on a charger.
- Establish whether the charger works.Another pack, another socket. Ten seconds of testing separates two very different problems and stops you buying the wrong replacement.
- Give it temperature time.Half an hour indoors, out of the sun and off a radiator. A great many not-charging complaints are packs charged the instant they came off the tool.
- Clean the terminals.Dry, gentle, no abrasives and no liquids. Grit and dust on contacts is a common intermittent cause, especially on a pack that lives in a site bag.
- Retire it properly if it is finished.Lithium packs are not household waste. Tape the terminals, keep it somewhere non-combustible, and take it to a battery recycling point or a tool retailer's collection scheme.
Tips
- Photograph the charger's light sequence and search the exact model number with the pattern described. The manuals are online even when yours is not.
- Fuel-gauge lights on the pack are useful diagnostics: a pack that shows nothing at all when the button is pressed is deeply discharged or dead, while one that shows a full charge and will not run a tool has a failed cell group.
- Keep the charger somewhere with clear air around it. Chargers on a shelf against a wall run hot, and heat shortens both the charger's life and the pack's.
If it doesn't work
No light on the charger at all
Cause: No supply, a failed lead or a dead charger — Fix: Try a different socket, check the lead and the fuse, and try a pack you know works. Chargers fail far more often than people expect, and a dead one looks exactly like a dead battery.
Steady light, or a slow pulse, and no charging
Cause: Temperature hold-off — the pack is too hot or too cold — Fix: Bring the pack to room temperature and try again. A pack straight off heavy work or in from a cold van is outside its charging window. This is protection working, not a fault.
Rapid flashing fault light
Cause: The charger has rejected the pack — Fix: Try a second pack in the same charger. If that charges, the fault is the pack. If it does not, the fault is the charger. This single test resolves most cases.
Pack was stored flat for months and now shows nothing
Cause: Cells below the protection circuit's minimum voltage — Fix: Some chargers have a recovery mode and will bring it back with a long slow trickle. Most will not, and a deeply discharged lithium pack is usually permanently finished.
Charges to partial and stops, or shows full immediately
Cause: One cell group failing, so the pack reaches its cut-off out of balance — Fix: That is end of life. A pack with a failed cell group will not recover and should be recycled rather than persevered with.
Intermittent — sometimes charges, sometimes not
Cause: Dirty or worn terminals, or a loose fit in the charger — Fix: Clean the terminals on both pack and charger with a dry cloth or a pencil eraser, check none are bent, and make sure the pack seats fully. Never use abrasive or wet cleaning on terminals.
Charger and pack both very hot during charging
Cause: Blocked charger vents, a hot environment, or a failing pack — Fix: Move both to a cooler place with clear air around them. If it recurs with a different pack, the charger is at fault; if it follows the pack, retire the pack.
Pack charges but runs flat in minutes
Cause: Capacity loss from age or cycles — Fix: Not a charging fault at all. The pack has reached the end of its useful life and needs replacing.
Questions people ask
Can I jump-start a dead lithium pack from another battery?
Do not. It is widely suggested online and it bypasses the protection circuit that is refusing to charge for a reason. Forcing charge into deeply discharged lithium cells is how they fail thermally.
Is a pack that gets warm while charging normal?
Mildly warm is normal, particularly on a fast charger. Too hot to hold comfortably is not, and it warrants stopping and letting it cool.
How long should a pack take to charge?
It depends entirely on the pack's capacity and the charger's output, and both are printed on the units. A pack taking far longer than it used to is usually a sign of ageing cells.