Battery care.

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Phil Pascoe

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I came across this looking for something else, and thought it might be of interest.
BEST PRACTICES FOR BATTERY LIFE
POWER TOOLS - BEST PRACTICES FOR LONG BATTERY PACK LIFE

1. IS IT BETTER FOR DEWALT® BATTERIES TO BE COMPLETELY DISCHARGED BEFORE CHARGING?
No. Just the opposite. You should stop using a battery as soon as you feel a substantial decrease in power from the tool. Completely running down a battery may damage it. Do not tape the trigger to run down the battery.

2. WHAT IS MEMORY, AND DO DEWALT BATTERIES HAVE IT?
Memory is one of many conditions which causes a loss of run-time. Memory is created from repetitive light use in the exact same application (i.e. Cordless Phones, Video Cameras, Electric Shavers, etc.) Our products rarely see light use or the exact same loads, due to variability from the user, the accessory size, as well as the material. The same variability which causes different run-times prevents our cells from developing memory. Power tools are considered high-drain applications. Memory typically develops in lower-drain rate applications, such as cordless phones, laptops, etc…, because the rate at which the battery is draining is continuously the same. Power tools draw higher currents and have sporadic drain rates minimizing the opportunity for the battery to develop a memory.

3. DOES IT HURT DEWALT BATTERIES TO LEAVE THEM IN THE CHARGER?
No. The DEWALT chargers have a maintenance mode which allows batteries to remain in the charger, maintaining a fully charged pack until the user is ready to work. If DEWALT NiCd batteries are stored outside of the charger, they will discharge naturally, 15-20% the first 24 hours, 7-10% the next day, and about 1% every day there after. NiCd batteries lose the bulk of the capacity when outside of the charger in the first 3 days. In fact, it is better for the battery to leave it in the charger to be sure it goes through Equalization and Maintenance Modes. One of the benefits of DEWALT XRP™ Lithium Ion batteries is that they have limited self discharge. Storing DEWALT Lithium Ion batteries outside of the charger will not result in loss of charge. Learn more about brushless tools technology.

4. WHAT CAN I DO TO IMPROVE THE RUN-TIME OF MY BATTERY?
If no permanent damage has been done to your battery, you may be able to improve its run-time.The correct procedure for charging your batteries is as follows:
1. Discharge the battery under normal use. Remove the battery, once you feel a loss of power from the tool. Do not tape the trigger ON.
2. Let the battery sit out of the charger for a least 2 hours until the battery is at room temperature.
3. Place the battery in the charger overnight to allow for a full charge on each individual cell (A minimum of 8 hours at room temperature).
If there is no difference in run-time, there is either permanent damage or the battery has reached the end of its usable life. In either case, the battery should be replaced.

5. DOES THE OUTSIDE TEMPERATURE AFFECT BATTERIES? HOW?
Yes. If the batteries are too hot (105°F or higher) or too cold (below 40°F), the batteries will not take a full charge. Attempting to charge batteries outside the 40°F-105°F range can result in a permanent loss of run-time. When batteries are being charged and discharged, a chemical reaction is taking place, and if it is too hot or cold the chemical reaction is disturbed causing a loss of run-time.

6. CAN THE DEWALT CHARGER BE USED WITH A GENERATOR?
Yes. All DEWALT chargers, excluding the DW9106, have been designed to handle the variations in voltage and current delivered by generators.


This is obviously Dewalt, other chargers might be different but other batteries aren't going to be.
 

Eric The Viking

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Phil I realise you didn't write the above (it looks like something from DW's marketing department), so none of what's below is aimed at you.

First key point: the cell chemistry (NiCd, Ni metal hydride, Lithium Ion, etc.) determines how you should manage them, in theory.

Second key point: some battery systems are clever, to the extent of charging individual cells in a battery one-at-a-time. Some are "really dumb", just applying charging volts to the whole battery and only measuring the drawn current. Many are in-between, measuring battery temperature (in some chemistries it's a reliable indicator of end-of-charge).

Third key point: Lithium Ion batteries, as used in mobile devices, CURRENT RANGES OF CORDLESS POWER TOOLS and Tesla cars (also mobile, I guess!) are SERIOUSLY picky about how they are charged. Get it wrong and they can explode. They are a lot harder to manage than older battery chemistry(s). You find Lithium Ion chemistry in 10.8V cordless tools from Bosch, Makita, DeWalt, etc. and probably in their larger battery packs. I'm pretty certain my Bosch 10.8v ones (three cells in each) charge the cells individually, as there are contacts to do that.

The screed above is also incorrect about NiCd batteries: it's BAD advice to leave those on the charger (also bad to let them completely discharge, though). They are unlikely to explode, but they will die if kept at fully charged state by trickle charging them. Lead-acid batteries (car battery chemistry) are the exact opposite - they die if not kept fully charged, but live long (and prosper) if kept at full charge carefully, which is why they are popular for things like emergency lighting.

Muddling the advice about two battery chemistries (NiCd and Lithium Ion), which have vastly different care+feeding requirements, is at best silly, and unhelpful. And anyway Lithium Ion batteries DO self-discharge, just more slowly than other technologies.

I have no idea how DW chargers of that vintage (old!) work but idea #4 is unlikely to work. Almost all batteries, irrespective of chemistry, die when one cell fails first. It then becomes a load on the other cells, and in simple Lead Acid and NiCd batteries becomes reverse-charged. If you can identify which cell it is (and replace it) the battery can be returned to use, but that involves careful dismantling and is slightly dangerous. Back in the days when milk floats ran on big lead acid batteries, the cells were individually packaged (car batteries have six cells in one plastic case), and could be repaired by swapping out individual cells. Similarly the much bigger batteries in telephone exchanges and lighhouses, etc. You could dismantle a NiCd battery pack too, test the cells and replace one or more failing ones. Modern Lithium Ion technology is too picky and nasty for this to be practical (unless you really know what you're doing!).

Phil's quite right: It's quite possible that DeWalt have chargers that use different circuits (and connections) for the different battery chemistries that they've sold down the years -- that would be fine. It won't apply to other brands though.

HTH,

E.

PS: As a general rule, modern Lithium Ion batteries last best if kept regularly charged. What does kill them, fairly quickly, is allowing them to go completely flat. My Bosch kit has safety cutouts to stop the batteries being over-discharged. If you stop when they cut out, wait a few secs and restart, you can get more work out of them, but this is a REALLY bad idea if you want the battery to have a long life.

My Bosch tools all have three LEDs for battery charge indication: switch batteries when there's only one bar left, and get the used one back on charge ASAP.
 

Phil Pascoe

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Thanks for that, Eric. My new Dewalt stuff has the indicator lights, as well. Interesting that NiCds shouldn't be kept on the charger - all my old Dewalt stuff was kept on charge permanently - 3 of the 4 batteries were fine when I sold the gear after 10 - 12 years. I wonder how much longer the failed one would have lasted if kept properly. :D

"It's quite possible that DeWalt have chargers that use different circuits (and connections) for the different battery chemistries that they've sold down the years -- that would be fine. It won't apply to other brands though."
I wouldn't think any major manufacturer used significantly different technology that another? Surmise - I don't know.
 

rafezetter

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I approve of Erik's post, and so does Spock - don't you Spock? *enigmantic nod*

Erik told me about this some time ago and I've tried to follow his advice since, and although I have no imperical evidence I'd swear my LI cordless batteries are giving me more life now that I'm charging them when they start to slow (just as DeWalt states apparently) instead of dead, they are Hitachi though not DeWalt.
 

novocaine

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Phil, you will quite likely find your 12 year old charger was relatively intelligent and actually shut off when it thought the battery was charged, so you were actually using the battery correctly without knowing.

I've killed a few drills, mainly because of pushing them past the flat limit, normally because I only needed a couple more screws, or a few more holes. now I buy with 2 batteries, one is on charge when the other is in use so I don't need to push past the low volt cutoff, so far it seems to work.
 

Phil Pascoe

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I've probably a good set up now - I have an 18v drill and jigsaw sharing two 2ah li-ion batteries. The full battery goes on whatever I'm using at the time, and the jigsaw fairly often uses it from full to flat. Just DIY not pro - I've never yet done so much with the saw as to flatten both batteries at the same time.
 

Eric The Viking

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Phil - I'm sure your DW charger was really clever. Actually, it probably just backed off if it spotted something pretty well charged.

The other thing is that batteries need well-matched cells in order to last. Quality brands will test and match cells (or at least sample production runs).

Cheaper batteries are probably made from batches of cells rejected from the quality end (what else will you use them for?). Of course even with those you might test individual cells to match them - matching is far more important than individual cell capacity. But I very much doubt it's done.

I've got an old right-angle drill which is really useful for jobs like kitchen cabinet fitting, where you often need to drive screws in a confined space. it's got a (rather daft) 18V battery, but it was cheap. It's NiCd, and at least one cell is almost dead. I'd love to re-cell it, but can't find a source of the correct size of tagged NiCds at a sensible price. It's an obsolete chemistry for practical purposes, so I'm unlikely to be successful now, which is a shame. As an amateur it's not worth buying a DW one for the rare occasions I'll use it, although it's a real get-out-of-jail-free type of thing.

Right PITA, but I might experiment with a laptop charger (19V usually) in case that will do - it doesn't really need to be cordless.

Generations to come will be so cross with us over "disposable" technologies!

E.

PS: Phil, as long as you "stop before flat", Lithium ion should go on for ages, depending on battery quality, obviously. My Bosch ones are still good after about six or seven years, and on a project they do get hard use (e.g. boarding out the loft).
 

Phil Pascoe

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I did read a long while ago that the very top end manufactures and Panasonic (being the cell manufacturer in this case) use the best matched and rated batteries. Some one did make a comment that it pays to evaluate the potential usage of a tool before purchase and buy one that is adequate not oversized - the more cells, the more likelihood of a cell failing - and it only takes one.
 

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