How to store and charge power tool batteries so they last

You charged it last week, you go to use the drill today and there is nothing in it, and the first thing most of us assume is that the battery has had it. Usually it hasn't. A lithium battery ages from how it is stored far more than from how hard it is worked, and a tin shed through a South Australian summer is about the worst place you can leave one.

I'm self taught on most of this, so I've worked it out the way I work everything out, which is getting it wrong first.

What actually wears a lithium battery out

Heat, and it isn't close

Heat is the one that does the damage, and it does it quietly while the battery is sitting still doing nothing. A shed with a steel roof gets a long way hotter inside than the air outside on a summer afternoon, so a battery parked in there is cooking every day whether you pick it up or not. The capacity you lose that way doesn't come back, which is why the runtime seems fine for two years and then suddenly isn't.

Sitting on full for months

A lithium cell is happiest somewhere in the middle. Charging one to full and using it that week is completely fine, that is what it is for. Charging a set of batteries to full in March and leaving them in a drawer until spring is the thing that quietly costs you.

If the tools are going away for a season, the number most manufacturers point at is somewhere around 40 to 60 per cent, so about half a charge. Two bars on the gauge rather than four.

Running it flat and leaving it flat

A battery that trips out mid job and then sits empty in the shed for six months can drop low enough that the charger won't wake it up again. That one is genuinely unrecoverable, and it is also completely avoidable by putting a bit back into it before you put it away.

Two old rules you can ignore

Don't store batteries on concrete. That is a real thing for old lead acid batteries and it does nothing at all for lithium, so a shelf is about keeping them off a wet floor rather than about chemistry.

Run it flat before you recharge it. Also real, for the nickel cadmium batteries a lot of us grew up with, which had a memory effect. Lithium has none of that, and it actually prefers partial discharges, so top it up whenever you like and stop feeling guilty about charging a half empty one.

What I'd actually do

• Keep the batteries in the house rather than the shed. A cupboard in the laundry is a better home for them than the bench they came off.
• Let it cool before you put it on the charger. A battery that is hot straight off a hard job and goes onto a charger is being stressed twice over, and 20 minutes on the bench costs you nothing.
• Take them off the charger once the light says they're done. Most chargers stop on their own now, but there's nothing to gain from leaving them sitting there, and anything left charging unattended for days is worth thinking about.
• Use the charger that belongs to it. A mismatched or cheap third party charger is not worth the risk on a pack that costs what these do.
• Take the battery out of the tool before it goes away, and wipe the terminals with a dry cloth now and then. Dust and grit on the contacts makes for a poor connection and a warm one.
• If a tool is going away for the season, leave the battery about half charged rather than flat or full.
• Look at a pack before you use it after a long break. One that has swelled enough to sit proud of the tool, or smells sharp, or gets hot on the charger, is finished. Stop using it and bring it in rather than chancing it.

Batteries are also the honest reason to stay inside one system rather than collecting brands. Every Katana 18V tool on our shelf runs the same Charge All battery, so the second tool costs you the skin and nothing else, and you aren't standing in the shed with four chargers and none of them fitting.

Shop related products

• Katana 18V Single Port Battery Charger. The plain one, for a single battery on the bench.
• Katana 18V Twin Port Battery Charger. Charges two at once, which matters when one of them is always in the tool.
• Katana 18V Cordless Hammer Drill, skin only. No battery in the box, because you already have one.
• Katana 18V Cordless Impact Driver, bare tool. Same battery again, for the screws that won't go in.

The rest of the range is in power tools.

Did you know we also stock the Katana 18V battery packs in store, in 2Ah, 4Ah and 5Ah, along with the Katana combo kits that come with a battery and charger in the box. They aren't on the website, so give us a ring on (08) 8536 4333 to check what is on the shelf.

More from the blog

• What an impact driver does, and when you need one
• How to anchor a bookshelf safely
• How to mount a TV flat and secure

Still learning this one myself, and my shed is not the shining example.

Cheers,
Candeece