Batteries - Is it OK to leave them in the charger?

[Stephen Tashiro]

Having owned DeWalt 18 V cordless tools for about two years, I finally got around to reading the directions for the battery charger. It says that after a battery is charged, 1 hour later the charger begins a process of "leveling" to equalize the charge on the cells. It says this should be done to batteries after 10 discharge-recharge cycles.

I tend to stick a discharged battery in the charger and leave it overnight. So my batteries get "leveled" on each charge. Is this good or bad for them?

[Ken Fitzgerald]

What does the manual say about leaving the batteries in the charger? Typically the manuals will tell you it's okay or DON'T DO IT.

[Ken Fitzgerald]

Stephen,I went to the Dewalt Website. Under Battery Technology I selected FAQs. There it says it will not do any harm to leave them in the charger.

[Stephen Tashiro]

Thank you. It's always a relief to know that a "bad" habit is at least OK.

[Jeffrey Makiel]

This topic has been flying around lately. The concern is more with the potential of starting a fire in light of recent manufacturer recalls (including DeWalt) and some posting of claimed events.

I've always thought that leveling off was important for NiCd batteries. Therefore, I always kept my chargers plugged in with a battery in them when not in use. The batteries failed seemingly prematurely anyway.

Now, I unplugged them after a few hours. I'm going to buy a 12 hour mechanical wall switch timmer at Home Depot and set it for two hours. This way, I won't forget.

It's more about peace of mind than battery life for me.

-Jeff

[Bob Slater]

Dewalt battery life is sub standard to start with. The worst part of owning their 18 volt systems.

[Prashun Patel]

I thought that old-style chargers can actually shorten the life of batteries if you keep the bats plugged in.

Most newer style chargers automatically switch to a trickle-charge mode which apparently does not harm the batteries.

That's hearsay; I can't tell from personal experience.

What I CAN say is that I've found that keeping the batteries in my drills tends to shorten the length of the charge. So, I always remove and cap them between uses.

[John Callahan]

I'd ditto Jeff's comments about the risk of fire. It's not something I though about much till a few years ago. A leg dropped out of the three phase at the place I was working at- all the cordless chargers were ruined. The circuit board in my Mak charger was melted. If I'm around, they're plugged in. If not, they aren't.

[Eric McMillan]

I've found with my Ridgid battery charger that if I leave the batteries in it, but the charger isn't plugged in, the batteries are completely dead the next time I try to use them. Apparently there's enough leakage back through the charger to totally empty the batteries. Something to watch for if using a timer to shut off the charger.

[Chris Tsutsui]

I really don't understand how a charger is able to equalize the voltage of cells when connected to a "pack" of cells. If anything, the charger just sends a trickle charge after an hour to top off any cells that didn't receive a full charge (thus "Maxing" each cell).

Even expensive matched cells do not have the same exact capacity, voltage, and aging. So although you are so called "maxing" the cells. Some cells will have a higher voltage and capacity than others.

If the dewalt charger is a peak charger which I think it might be, then it charges the battery while monitoring the voltage. When the voltage ceases to increase in the overall pack then the charger stops charging and begins to trickle charge while it's stored. This keeps the battery with a maximum charge as long as it's connected to the charger.

Though If this is the case and the battery is being sent a trickle charge while it's being stored then I wouldn't plan on keeping the battery connected TOO long. (Such as leave it in there for more than a day)

By trickle charging a battery too long after it's already charged, you risk decreasing the overall life of the battery.

[Stephen Tashiro]

I, likewise, don't understand how the charger can equalize the charge per cell. DeWalt's terminology for this process is the trademark phrase: "Automatic Tune-Up".

[Chris Padilla]

http://www.sawmillcreek.org/showthread.php?t=114328

There is a whole discussion of this going on in the Workshop Forum right now. Join in...or just peruse!

[George Morris]

I had a dewalt 18v charger melt and started to smoke. Thank goodness someone was at home when it happened. I got a new charger and battery from dewalt but could burnt down the house.

I will never charge any battery unless I am at home to keep a eye on it!! Take it for what it is worth!! George

[Bill White]

This issue is a wierd one in that there never seems to be a REAL answer, so......
Charge it, take it off the charger, unplug the charger----That's my process.
Bill

[Byron Trantham]

I have a 9.6 and a 14.4 DeWalt drill. In 2005 my 9.6 stopped working and it never did run that well new. I sent the two battery packs to Primecell for rebuilding. At that time they cost $25/pack. When I got them back I was astounded! They were so much more powerful and they have been in heavy use every since and still going strong. I bought a 14.4 (XRP model) a couple years later. Again, after about a year no poop. Sent them in and again the results were terrific. I talked to them about care. They told me the biggest enemy of a battery is HEAT. No matter what the mfr. says about leaving your battery in their charger don't leave it in for days at a time. The battery remains warm and never cools off. What I did was go the borg and bought one of those cheap mechanical timers. You know the ones with a big dial and a couple pins you put in the wheel to start and stop the timer. I placed the pins so that it would turn on my charger for forty minutes and then turn it off. If I forget to take the battery out, no biggie, 24 hours later it will charge for another 40 minutes. Basically I plug in the charger and rotate the timer dial until it clicks. Forty minutes later - charged. Back to the heat issue. When you are using a battery and trying to get "that last few screws" in and the drill is laboring- STOP! At this point the batteries are pretty warm. Pull it and put in the other charged battery. Do not put the old one in the charger until gets a chance to cool down. The 2005 rebuild is still going strong and I always have a fresh battery. BTW I do unlpug the timmer when I don't need it.