Pack Charge Time Calculator
Estimate how long a tool pack takes to charge, from its amp-hours and your charger's output.
Charge time is roughly the amp-hours you need to put back, divided by the charger's output in amps, plus extra time at the end while the charger slows down to top off the cells. Everything is worked out in your browser. Nothing is saved or sent anywhere.
1. Your battery pack
Use the amp-hour rating printed on the pack.
The fuel gauge gives a rough figure. One bar of four is about 25%.
2. Your charger
The output current is printed on the charger label, usually as "Output: 18V ⎓ 4.0A" or similar.
Extra time for the slow end of the charge and losses. 20% is a sensible starting point.
3. Results
How it was worked out
What this does and doesn't tell you
- This is an estimate. Chargers slow down or pause when a pack is hot or very cold, and some won't start until the pack has cooled. A pack straight off a hard-working tool can take much longer.
- A fast charger only charges at full speed if the pack and charger are made to work together. Some chargers limit current for smaller packs.
- If the charger flashes, refuses the pack or never finishes, that's usually the pack or charger protecting itself. See Charger Lights and the BMS.
- Lithium-ion tool packs can short, overheat and catch fire if they're damaged, wired wrongly or charged on the wrong charger. Only use the maker's charger for the pack, and recycle any pack that is swollen, burnt, leaking, crushed or has been in water.
Next steps
Work out how long that charge will last on the tool with the Pack Runtime Calculator, or read Why Won't My Pack Charge? if something isn't right.