Cordless Charger Timer

[Jon Amsden]

I used to race battery powered electric cars. While I was running them we went through a big technological shift from NiCads to NiMH so I only speak for those batteries. Our chargers were pretty darn advanced and even those did not appreciate us unplugging their power source.

If was fairly common that breakers would be popped in the pits and our chargers had alarms in them to tell us when they lost power because it would reverse drain our batteries. This would certainly shorten the life of our very expensive batteries. Mind you, we were charging our packs at very high rates and draining them at very high rates.

I can't speak to what will happen to your batteries, but I would not do that given my experience.

[Tom Esh]

My Makita 18V batteries will drain while on the charger if I unplug it. I've done it couple times by accident.

Leaky rectifier(s) cause that. They can be that way to start with or become leaky with age. That's why I never leave a bat on an un-powerd charger. Years ago it cost me a very pricey strobe pack before I figured out what was happening. Unfortunately since the symptoms are often exactly the same as a bat that won't hold charge, the only way to tell is to rig a meter in the circuit.

[Larry Edgerton]

Some chargers will deplete a battery if left in the cradle, turned off! A rude awakening if you expect a fully charged battery and it is completely dead. IF...this is not the case, Glenn's is a viable solution. IF this IS the case, a good reason corded power tools are still very usable!
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I had a problem with my Hilti's when people [painters]would unplug and and leave the batteries on the charger. According to the Hilti rep in that case the battery was backfeeding and essentually running the charger, so by the time they set a couple of days the batteries were junk.

Painters!

[Rick Christopherson]

They actually state that a battery will loose up to 20% of its charge in the first 24 hours off the charger, 7-10% the following day and about 1% every day after that.

This statement pretty much sums up the validity of the whole article. If DeWalt batteries are loosing 30% of their charge in the first 48 hours on the shelf, that is not exactly the tool I would want to own. DeWalt doesn't manufacture their own batteries (to the best of my knowledge), they use the same batteries as everyone else.

According to their numbers, a battery will be stone dead in 60 days. I have so many Festool drills and batteries floating around that it is not uncommon for a battery to sit for well over six months before I need to use it, and still have plenty of power operate the drill for several hours.

I believe my Makita manual says leave it in the charger. Of course Makita is also in the business of selling new batteries.

This maintenance mode is OK for short term storage, but it is not intended for long term storage--see below.

I leave my Festool batteries in the chargers continuously charging so that I always have a fresh battery. I've been doing this since day 1, 5 years ago. The key is the battery charger, I think. One set of batteries for my TDK-15 drill finally died and I've had both rebuilt but the other set for the CDD-12 drill is still going and it older than the TDK by at least 1 year...maybe 2!

I can't speak for Makita chargers, but I can for Festool chargers. Even though these are intelligent chargers and designed to use a maintenance mode, it is not intended for long term storage. This has been confirmed with Festool service. The Festool chargers are probably the most intelligent chargers on the market, but I wouldn't leave an expensive battery in the charger past 1 week. The new Li-Ion chargers for the T12/T15 are different, and with these, the battery should be left in the charger, but I don't know if that applies to non-Festool Li-Ion chargers.

If you guys knew how the technical publications industry worked, you wouldn't be so quick to say, "but the manual says..." There are some writers that are savvy and understand what the words on the paper mean, but the vast majority of them don't, and that is how misinformation finds its way into manuals.

[Thomas Syrotchen]

Rick,

The discharge rate Dewalt state is not out of line with other published numbers on the discharge rates of NiCd batteries. While it is on the high end, they are still reasonable numbers when you consider that the low end of most published numbers for a discharge rate is 10% for a new battery and at 30% a battery is unlikely to hold a charge. Since discharge rates are based on a number of factors, including temperature and battery condition that will alter those rates considerably a battery may last six months on the shelf and it may last 6 weeks. However, it doesn't change the fact that NiCd batteries will discharge at the greatest rate in the first 24 hours sitting on the shelf. It doesn't matter what logo you slap on the side of the battery, if it utilizes NiCd technology it will have a high discharge rate when initially removed from the charger.

I wouldn't doubt that Dewalt's recommendations came on the assumption that the majority of their market regularly uses their batteries and by allowing it to remain on the charger, it will complete a maintenance cycle which should increase battery life. Since the original post showed a timer system that left the battery on a charger with no power applied, the link to Dewalt’s response to the FAQ regarding leaving a battery on a charger. Please also note, that two of the three chargers pictured are Dewalt’s chargers so it made sense to post a link to their site which clearly states that leaving it on an unplugged charger is not recommended. As other’s have posted, it will likely lead to a more rapid discharge of the battery. I think others can verify that electrically, this is a sound principle.

There is no one all encompassing answer to the question "Should I store my battery on the charger". It depends on the design of the charger, the frequency with which the battery is used, the temperature in the room their stored in, and the condition of the battery. As you pointed out, consulting the manufacturer is probably the best option. If it’s a situation where you don’t use the battery but every six months, then leaving it off the charger probably makes more sense. However, if you are using the battery on a regular basis and have a smart charger it probably makes more sense to leave the battery on the charger. I agree 100% that leaving a battery on a charger for several days at a time may lead to premature failure as well. Again, it all depends on several factors and one should consider those in deciding which is the best option for their situation.

[Chris Tsutsui]

I love the idea of a physical timer on the charger. In an ideal situation, the timer would disengage two connections. One connection the charger has with the wall outlet. The other connection being with the battery and the charger.

I'm sure a timer could be introduced tapping into a wire in the charger near the point it connects to the battery.

This would be the best of both worlds... A peak charger that has timer shut-off. Set it, and forget it...

[Matt Meiser]

Regardless of the leaving batteries in or out of the charger debate, I try to remember to shut mine down just for the reason that a guy in our club had a major house fire that started in his shop. They traced it back to a battery charger and the insurance adjuster told him that that wasn't the first one he'd seen. The odds are pretty small of it happening, but adding a timer to shut them off, or even remembering to unplug them 1/2 the time reduces the odds greatly.

Another reason to shut them down is that they are always consuming energy.