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I have a set of Dewalt cordless tools with both 18V NiCad and 20V LiIon batteries (I also have an adapter that lets me use the 20V batteries in the 18V tools). The tools are only a few years old, and the drill and impact driver both have LED lights to illuminate your work area. The LED lights when depressing the trigger slightly.

I used both the drill and impact driver one day and then left them overnight. Both tools are 18V; I used an 18V NiCad in one and the 20V LiIon (with adapter) in the other. I went to use them again the next day, but both batteries were dead. The direction / safety switch on both was set to "off" and the tools were not used, so I was surprised to find the batteries depleted. Aside from the inconvenience, is this bad for the battery or the tool? Does this indicate a problem with either?

The tools and batteries are normally stored / charged in my garage, so they've been exposed to some colder temperatures (nighttime lows of 40F typically, though some nights as low as 25F) recently, which can affect battery charging. Days have typically been relatively warm (at least 60F).

  • No personal experience, so ymmv, but have heard that the 18>20 volt adapter does kill batteries in its spare time. I can't explain the 18v impact and the 18v battery, and I've had 18v dewalt in rotation for >10 years, with scandalous quantities of tools and batteries. – Aloysius Defenestrate Jan 31 '17 at 1:01
  • Temperature swings can affect battery performance. Also a charge cycle, especially a NiCad battery, can affect performance. LiIon batteries are said to not have such a memory effect, however they do. After about 5 years my LiIon laptop battery will only power for 15 minutes unplugged. So many factors can affect a battery. – Jeff Cates Jan 31 '17 at 1:53
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    As long as the trigger is not activated it should not affect the battery at all. I try to put my dewalt tools in the locked position so when they are bouncing around in a bag or truck they don't turn on and drain the battery that has happened a time or two in the past. If you put the direction control in the center and pull the trigger the light should not come on. Recently the temps have been in the low teens and I did not notice my 20V LiIon battery's loosing charge but cold weather can affect them. – Ed Beal Jan 31 '17 at 14:08
  • No you should not have any problems. – Mike Jan 31 '17 at 17:12
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Most drills (all the ones I know about) have a physical switch that connects to a relay that actually completes the circuit that will get the drill to spin (like in this circuit). So unless there is a display or something that requires constant power (like if those LEDS had their own switch) the batteries should hold their charge as long they are chemically able to do so. The NiCad battery may have issues maintaining its charge compared to the LiIon battery but you should not be able to tell the difference after one day. Even though neither of them should be dead after one day.

The LiIon battery may have been close to dead without you noticing since they tend to put out a constant voltage even while at low power levels; however, the NiCad should have showed some signs of being low.

Regarding the weather, NiCad should be able to tolerate the cold fairly well. LiIon on the other hadn can have damage to the cells from really cold temperatures but i've left tools out overnight in freezing weather (0F-10F) many times and once they warmed up a bit they worked fine (ignoring the fact I probably lowered amount of recharge cycles they had left).

All that being said I also think its really unlikely that both batteries/ drills (or any combination of the 4) have issues... So other than the fact you angered the pixies living in your tools by leaving them out in the cold, I would guess the long term storage in a place with large temperature changes shortened the capacity of your batteries.

PS The reason LiIon batteries are stored at roughly 40% capacity is that part of the trade off of being able to have a bunch of small charge cycles going up and down a lot (like cell phones) is the fact they don't do too well at the extremes (0% & 100%) because one way chemical changes are more likely to happen (lowering their capacity and cycle life).

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Easy test is to charge both batteries and repeat the experiment.

If it happens again, then there is a discharge going on, but as stated above, theoretically "OFF" is "OFF", or else the companies would be getting a whole lot of complaints.

Nicads, after a while do 'self-discharge but this is normally when the battery life is about exhausted and chemically they cannot hold much of a charge anyway, but this doesn't seem to be the case here.

  • Hello, and welcome to Home Improvement. Thanks for the answer; keep 'em coming. And, you should probably take our tour so you'll know how best to contribute here. – Daniel Griscom Aug 10 at 16:00
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No, the tools themselves are unaffected by rechargeable lithium or nickel cadmium battery packs. Alkaline batteries can carrode/leak over time, but I have never seen a this happen with any type of NiCd/Li battery pack.

HOWEVER.... there is (supposedly) a reason why most battery packs are sent half-charged. Supposedly the batteries themselves do better in long term storage at half capacity. I have yet to actually witness any useful validation of this urban legend.... I think it's just an excuse for manufacturers to only charge them halfway. I am sure there is some valid argument supporting their positions based on the internal chemistry, but in the real world it doesn't seem to make any difference.

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