Li-ion batteries in drill/driver

[petek]

Happy Christmas all! I've been given a Bosch GSB120-Li drill/driver as a pressie for Christmas with two 12v 1.5Ah Li-ion batteries. This is the first Li-ion battery tool I have had and have previously relied on my 50+ year old corded B&D for my occasional DIY use, but it's now on it's last legs. I'm unsure how best to look after the batteries. How long can I leave a fully charged battery in the drill without use before the battery charge deteriorates? Can I leave a partially charged battery in the drill for long periods? How long will the alternative battery remain fully charged? Should I leave a battery in the charger, switched on, while not being used? Should I periodically recharge both batteries? Do I have to fully discharge the batteries before re-charge? The instruction manual is no use in answering these and many other questions I have so any advice would be appreciated.

Cheers Pete

[John Rumm]

and to you...

LiIon batts are different beasts from the NiMh and NiCd batteries of the past. They don't suffer so many of the drawbacks like high auto discharge etc. They do however need careful management in use and when charging and so typically contain battery management modules that do this.

A significant time, and it will retain a charge. Might be worth giving it a partial refresher charge once a year if not being used.

They are affected by temperature during storage. Prolonged periods over

55 deg C can ruin them, and below -15 can cause them to discharge.

Yes

Similar amount of time or a bit more. There are some management electronics in the battery that will take a tiny current even when not in use.

You can - the chargers are smart and communicate with the battery. They will only charge it until "done" and then stop.

Only if left a very long time. Bosch normally suggest not fully charging before storage though since they are more "active" when fully charged and that causes faster ageing.

No. Some of the less sophisticated systems may simply count the number of times they are mounted on the charger as a "cycle". So frequent partial charges may accelerate the point at which the battery management system thinks the battery has reached end of life.

[The Natural Philosopher]

More or less indefinitely. The ideal state to store li-ion is half charged. But in reality that's pretty impractical. The rate of self discharge is far far lower than any nickel chemistry.

If you are using them regularly keep them fully charged, If not well you could always out them away in whatever state of charge they ended up I suppose.

See above. That is the ideal state.

I typically see maybe a 10% drop in charge over a year on my model aircraft batteries - 5% over the winter.

Most chargers will switch off when the battery is charged. On my cheap cordless an LED turns green...so there isn't much point in leaving the batteries in..

No. Its pointless.

No. Its not that good for them although the drill circuitry would stop over discharge

[Theo]

Generally I'd suggest not overthinking things. The battery contains a circuit to protect it from getting overdischarged, cooking itself, and the charging system takes care of preventing it overcharging.

So just use it however you need. In general however there are a couple of points to bear in mind for optimal life:

- batteries are happier if they're not 'full' or 'empty'. So if you need to store for long periods, leave them somewhere in between. 40% is a typical storage charge, although 80% is still fairly easy on the battery ( most power tools don't have a gauge good enough to read this - you can use a voltmeter if you need to, if you look up the lithium ion battery curves).

- when you use it under heavy loads, it gets warm. It's better to minimise the warming (eg have a tea break, or swap to another battery), and to let the battery cool before charging.

You can happily ignore these 'rules' and get many years life out of them - they're more of a concern for big batteries that have to last for many years of daily use, like those in electric cars. Unlike cars, power tools don't have automatic ways of mitigating them (no liquid cooling in a drill).

Theo

[petek]

Thanks to all three of you for the clear advice, which has set my mind at rest considerably. All the best for the New Year - it can't be any worse than the last one!

[John Rumm]

That was historically good advice, but these days runs counter to what the makers suggest when they have cooling systems in the chargers. So with the Makita for example, they say that hot batteries should be put on charge ASAP. The chargers read the battery temperature and use the built in cooling fan to pass air through the battery. They don't actually start charging until the temperature has been brought down to an appropriate level. They then fast charge (and cool), and continue to cool after charge for a while.

The battery management system will shut down the drill if the battery gets too warm.

[Theo]

That sounds a level beyond my cheapass Aldi tools :)

I have NiMH and 18650 chargers with a fan, but nothing else does - they're just wallwarts with a battery cradle attached.

'too warm' meaning 'about to catch fire' rather than meaning 'will reduce battery life by 25%', I suspect.

Theo

[alan_m]

You may also find that you don't notice a drop off in performance of the drill and then the protection circuits will just remove power from the battery just before being discharged. You will not necessarily notice the battery close to the end of charge before the drill cuts out completely.

[ARW]

Forget all this stuff about batteries..................

Who's bought you such nice presents and what DIY tasks do they want you to do for them in return?

;-)

[Murmansk]

That model of drill has a battery gauge consisting of a row of LEDs and it's reasonably accurate so you could probably use it to estimate when the battery is half full for storage and also to get reassurance that next time you use it it's going to actually be able to function

[The Natural Philosopher]

Correct. I've run my cheapo cordless down several times. Just slows to a crawl, and then refuses to start at all. Within seconds

[Dave Plowman (News]

With Lidl ones, the battery itself seems to contain a great deal of electronics. Be interesting to see a block diagram of the entire unit - drill battery and charger.