How long should cordless tool batteries last?

People ask this expecting a number of years, and the honest answer has two parts. A lithium pack loses capacity every time it is cycled, and it also loses capacity simply through time, faster when it is hot and faster when it is held at full charge. A trade user hits the cycle limit; a home user almost always hits the calendar limit first, and how they store the pack decides when.

Step by step

1. Count cycles, not charges.A cycle is a full charge's worth of energy, so two half-charges count as one. Topping a pack up frequently does not use it up faster, which is the opposite of what most people assume.
2. Expect gradual loss, not sudden death.Capacity fades progressively. A pack does not fail on a particular day; it gets shorter and shorter until you notice, which is why the decline is easy to miss.
3. Recognise calendar ageing.A pack degrades in storage, driven mainly by temperature and by state of charge. Full and hot is the worst combination, half charge at room temperature the best.
4. Identify what shortens the life most.Heat above everything: charging a hot pack, storing in a loft or a car, working it hard without letting it cool. Then deep discharge, then storage at full charge.
5. Set realistic expectations for a home user.Occasional DIY with sensible storage: five to eight years is entirely normal and longer is common. Trade use every day: two to four years is more typical, and that is the cycle count doing it.
6. Know when to replace rather than persevere.When runtime is a fraction of what it was, when the tool cuts out under moderate load, or when the pack heats up quickly during charge or use. Any of those means it is finished.
7. Buy packs when you need them, not in advance.A spare pack bought now and stored for three years will have aged whether you used it or not. Buying ahead does not preserve anything.
8. Check for a registration scheme.Several manufacturers extend battery warranty on registration within a short window after purchase. It costs nothing and it is the one piece of admin worth doing on a new tool.

Tips

• A pack that gets noticeably hot in normal use is telling you its internal resistance has risen. That is an ageing sign and it accelerates, so plan the replacement rather than waiting for it to fail mid-job.
• Most packs carry a date code. If you are buying spares, a pack that has been sitting in a warehouse for two years has already used part of its calendar life.
• When a platform is nearing the end of its life, the sensible calculation is often a new tool kit rather than two replacement packs. Compare both before deciding.

Keeping on top of it

• Store packs at around half charge, at room temperature (whenever they go away for more than a few weeks)
• Top a stored pack back to about half charge (every three to six months)
• Let a hot pack cool before charging (every time)
• Wipe terminals and check for damage or swelling (a few times a year)
• Bring packs indoors before winter (annually)

Questions people ask