DeWalt battery not charging

[1190R]

My 9 AH battery wont charge

It's got one light on so not completely dead

Opening the battery case reveals no obvious broken welds or other visible problems

How to troubleshoot?

I have already received a replacement from DeWalt because it is under warranty but nevertheless want to fix this one

 

[johnre]

What about the charger - do you have a spare battery you can use to test it?

 

[toolenthusiast]

If it has some power and won’t charge, that probably means the cells are unbalanced. The major power tool brands do not have cell balancing in their chargers.

 

[1190R]

What about the charger - do you have a spare battery you can use to test it?

I have 6 chargers and they all work with my 10+ other batteries

 

[1190R]

If it has some power and won’t charge, that probably means the cells are unbalanced. The major power tool brands do not have cell balancing in their chargers.

How to rebalance?

 

[lund]

I have had that situation before and I used a relatively low value resistor connected between the power terminals to completely drain the battery and then put it back on the charger and it cycled correctly. Some say to do that with a short between the terminals, but there is a lot of energy in lithium-ion batteries and I would use caution if you do that ... something to limit current is wise. I recommend doing this type of stuff outside, using safety glasses, and having an electrical style fire extinguisher ready. It can be shocking how lithium ion batteries can burn when ignited. I often wonder how many homes will burn down with hybrid/electric cars.

 

[1190R]

I have had that situation before and I used a relatively low value resistor connected between the power terminals to completely drain the battery and then put it back on the charger and it cycled correctly. Some say to do that with a short between the terminals, but there is a lot of energy in lithium-ion batteries and I would use caution if you do that ... something to limit current is wise. I recommend doing this type of stuff outside, using safety glasses, and having an electrical style fire extinguisher ready. It can be shocking how lithium ion batteries can burn when ignited. I often wonder how many homes will burn down with hybrid/electric cars.

Maybe I'll try running the battery down in a tool first. I was trying to avoid that because many YT videos say batteries won't charge if completely depleted. If completely draining it with a tool doesn't work what size resistor do you recommend?

 

[GeoBruin]

I have had that situation before and I used a relatively low value resistor connected between the power terminals to completely drain the battery and then put it back on the charger and it cycled correctly. Some say to do that with a short between the terminals, but there is a lot of energy in lithium-ion batteries and I would use caution if you do that ... something to limit current is wise. I recommend doing this type of stuff outside, using safety glasses, and having an electrical style fire extinguisher ready. It can be shocking how lithium ion batteries can burn when ignited. I often wonder how many homes will burn down with hybrid/electric cars.

According to data from the National Transportation Safety Board used to track the number of car fires and comparing it to sales data from the Bureau of Transportation Statistics, car fires are over 61 times more likely to occur in an ICE vehicle than an electric vehicle.

https://www.kbb.com/car-news/study-electric-vehicles-involved-in-fewest-car-fires/

 

[lund]

According to data from the National Transportation Safety Board used to track the number of car fires and comparing it to sales data from the Bureau of Transportation Statistics, car fires are over 61 times more likely to occur in an ICE vehicle than an electric vehicle.

https://www.kbb.com/car-news/study-electric-vehicles-involved-in-fewest-car-fires/

Interesting stat, thanks. But I am not so sure it tells you what you may be inferring on electric being 61x safer for fire if that is what you mean. You do not want any kind of car (gas, hybrid, electric) burning in your garage. Fires are relatively low frequency events ... but with potentially problematic outcomes when they occur in homes/garages. Burning on the road after an accident after any injured people are evacuated is likely less problematic. But you can be killed when a car goes up in a garage if you are unlucky (sleeping) and the alarms do not work well enough or are insufficient to rouse you.

I would be willing to bet in terms of gas car *garage fires* that it is mostly older cars if gas leaks with vapor ignition sources near (heater etc). There are plenty of old gas cars so I would assume the distribution of ages of gas cars in garages is roughly constant as people buy new ones and old stuff is retired/scrapped. Electric cars are mostly a newer thing AND old battery packs may become much more problematic than newer battery packs. I would watch carefully how the statistics of garage fires evolve as more electric cars fill garages. Also, if you have solar with battery banks, I would be cautious about having large battery banks inside your home.

You can google videos of electric car fires to see what I mean on burn intensity. Yes, it is similar for gas. But you do not want these burning in a garage. Airlines are fairly stressed over the proliferation of large capacity lithium ion batteries in luggage since the consequence of such fires (even if smaller) in confined spaces can be problematic.

 

[lund]

Maybe I'll try running the battery down in a tool first. I was trying to avoid that because many YT videos say batteries won't charge if completely depleted. If completely draining it with a tool doesn't work what size resistor do you recommend?

I am not sure how complete the drain will be by running. I wanted it stone dead discharged to reset fully in the charge cycle. That worked in my case. I measured the terminals with a voltmeter to find the power pins (can also find online) and jumpered a resistor between. Just use Ohm's law: I = V/R where I is the current in Amps, V is the voltage in Volts, and R is the resistance in Ohms and keep the current reasonably low (say fraction of an amp). I think I used the battery pack voltage of 20V (was less than this) and selected 500 Ohm resistor => 40 milliAmps max. But anything even much smaller would be fine ... just wait longer for full discharge. A length of heater wire from an electric type space heater (much lower resitance) could also work. Low current is fine and safe for this though. Some argue that a rapid discharge (via short circuit) helps burn out potentially problematic zones in the battery cells ... but I am skeptical on this and if you short it, be more careful how and where you do it.

Hope this helps.

 

[1190R]

I am not sure how complete the drain will be by running. I wanted it stone dead discharged to reset fully in the charge cycle. That worked in my case. I measured the terminals with a voltmeter to find the power pins (can also find online) and jumpered a resistor between. Just use Ohm's law: I = V/R where I is the current in Amps, V is the voltage in Volts, and R is the resistance in Ohms and keep the current reasonably low (say fraction of an amp). I think I used the battery pack voltage of 20V (was less than this) and selected 500 Ohm resistor => 40 milliAmps max. But anything even much smaller would be fine ... just wait longer for full discharge. A length of heater wire from an electric type space heater (much lower resitance) could also work. Low current is fine and safe for this though. Some argue that a rapid discharge (via short circuit) helps burn out potentially problematic zones in the battery cells ... but I am skeptical on this and if you short it, be more careful how and where you do it.

Hope this helps.

Ok

Battery completely drained

Now charger light does not even blink when battery inserted

What to try next?

 

[GeoBruin]

Ok

Battery completely drained

Now charger light does not even blink when battery inserted

What to try next?

Your charger will definitely not charge the battery when it's completely dead. You will need to jump start the battery with another battery just like you would jump start a car battery. The goal is to give it just enough charge to reach the minimum threshold where your charger will be able to start charging it.

The tricky part is that charging lithium ion batteries at too high a current when they're overdischarged is a recipe for disaster. I don't know what the internal resistance of that pack is but it might be good to put an amp meter on it when you start the jump start process and make sure you're not charging it at too high a current.

There are about a million YouTube videos of people jump starting their dead batteries but you never know if you have the same starting conditions as everyone else so you just need to be vigilant.

 

[lund]

Ok

Battery completely drained

Now charger light does not even blink when battery inserted

What to try next?

Not sure. You could have a bad cell and the charger may have protection. It should not be the case that a completely discharged cell will not charge. But their can be protection wired in for bad cells and that may be triggered.

You may need to remove individual cells and check ... if you want to try more to repair. I am not sure how much trouble it is will be worth.

 

[1190R]

Your charger will definitely not charge the battery when it's completely dead. You will need to jump start the battery with another battery just like you would jump start a car battery. The goal is to give it just enough charge to reach the minimum threshold where your charger will be able to start charging it.

The tricky part is that charging lithium ion batteries at too high a current when they're overdischarged is a recipe for disaster. I don't know what the internal resistance of that pack is but it might be good to put an amp meter on it when you start the jump start process and make sure you're not charging it at too high a current.

There are about a million YouTube videos of people jump starting their dead batteries but you never know if you have the same starting conditions as everyone else so you just need to be vigilant.

Did that

Back to one bar but still wont charge

 

[1190R]

Not sure. You could have a bad cell and the charger may have protection. It should not be the case that a completely discharged cell will not charge. But their can be protection wired in for bad cells and that may be triggered.

You may need to remove individual cells and check ... if you want to try more to repair. I am not sure how much trouble it is will be worth.

Well, they're more than $200 at HD and then there's the challenge

Hoping someone here has brought one of these back to life

 

[Rabid Badger]

First step is to remove the case and check the voltage of each group of parallel cells. I'm not 100% sure how to do that on a battery that can reconfigure itself, though.

Once you figure out which groups are low, you need to charge them slowly with a bench power supply.

Do NOT try to charge them by connecting them to another battery. That's what idiots do.

 

[1190R]

First step is to remove the case and check the voltage of each group of parallel cells. I'm not 100% sure how to do that on a battery that can reconfigure itself, though.

Once you figure out which groups are low, you need to charge them slowly with a bench power supply.

Do NOT try to charge them by connecting them to another battery. That's what idiots do.

Got an example of a reasonably cheap bench power supply?

 

[Rabid Badger]

Got an example of a reasonably cheap bench power supply?

This one should do the trick:

https://www.amazon.com/Jesverty-Variable-Switching-Quick-Charge-Adjustment/dp/B0DDPVDWPZ?tag=atomicindus08-20

You might see cheaper units, but don't buy anything that doesn't have a button to enable the output.

 

[Dakotadadv8]

Jump start then charge. Worked on Dewalt 8 year old and 1 year old battery.

 

[lund]

Your charger will definitely not charge the battery when it's completely dead. You will need to jump start the battery with another battery just like you would jump start a car battery. The goal is to give it just enough charge to reach the minimum threshold where your charger will be able to start charging it.

The tricky part is that charging lithium ion batteries at too high a current when they're overdischarged is a recipe for disaster. I don't know what the internal resistance of that pack is but it might be good to put an amp meter on it when you start the jump start process and make sure you're not charging it at too high a current.

There are about a million YouTube videos of people jump starting their dead batteries but you never know if you have the same starting conditions as everyone else so you just need to be vigilant.

Why are you saying a battery charger will not charge a completely dead battery? Mine charged when I did a full discharge of a Lithium Ion battery pack (20V) when I had an issue. IF the pack has a dead cell in it, yes that could trigger a protection mode. But it would be a stupid circuit if it shuts down completely and identifies a full discharge as defective. A charger should be current limited and drop the voltage (with the current dropping as a function of voltage with the cell charging characteristics) when strongly discharged. It is pretty bad engineering if (some?) brands of chargers are refusing to work at their max charge rate from a fully discharged state. It makes me wonder if they just want packs thrown out under circumstances where anything is atypical due to potential liability. Lithium ion batteries can be dangerous when overheated etc and you could do that at a prolonged high charge rate with a damaged cell. Care is certainly in order when tinkering with battery packs. The stored energy can be substantial. Some of the stuff you see online with people claiming to "jump start" dead batteries with short to burn out bad zones seem imprudent at best and as you point out could get wildly different results depending on the nature of the issue and small details of how you jumper things etc. But conversely, if you can identify a bad cell and replace it using reasonable care with the right tools (soldering skills etc), I do not see why it should be so problematic. Of course the manufacturers will tell you not to do that since they do not want to be blamed with anything stupid done and they would rather sell replacements and have you throw a full pack away.

 

[GeoBruin]

Why are you saying a battery charger will not charge a completely dead battery? Mine charged when I did a full discharge of a Lithium Ion battery pack (20V) when I had an issue. IF the pack has a dead cell in it, yes that could trigger a protection mode. But it would be a stupid circuit if it shuts down completely and identifies a full discharge as defective. A charger should be current limited and drop the voltage (with the current dropping as a function of voltage with the cell charging characteristics) when strongly discharged. It is pretty bad engineering if (some?) brands of chargers are refusing to work at their max charge rate from a fully discharged state. It makes me wonder if they just want packs thrown out under circumstances where anything is atypical due to potential liability. Lithium ion batteries can be dangerous when overheated etc and you could do that at a prolonged high charge rate with a damaged cell. Care is certainly in order when tinkering with battery packs. The stored energy can be substantial. Some of the stuff you see online with people claiming to "jump start" dead batteries with short to burn out bad zones seem imprudent at best and as you point out could get wildly different results depending on the nature of the issue and small details of how you jumper things etc. But conversely, if you can identify a bad cell and replace it using reasonable care with the right tools (soldering skills etc), I do not see why it should be so problematic. Of course the manufacturers will tell you not to do that since they do not want to be blamed with anything stupid done and they would rather sell replacements and have you throw a full pack away.

A lithium ion cell is considered fully discharged at around 2.7 volts per cell, and fully charged at around 4.2 volts per cell. The low voltage cutoff curcuit in either the tool or the battery (depending on brand) will typically stop the tool from discharging below that point. However, if a battery does get discharged below that point (self discharging from sitting for a long time, used in tools that don't have a low voltage cutoff circuit, etc.) the charger will recognize that as a trouble state and will not charge.

That's why "jump starting" batteries is a thing. You can charge a battery up just enough from connecting it to another battery with a higher charge state that you can bring it back above the threshold where the charger will charge it again.

 

[1190R]

Why are you saying a battery charger will not charge a completely dead battery? Mine charged when I did a full discharge of a Lithium Ion battery pack (20V) when I had an issue. IF the pack has a dead cell in it, yes that could trigger a protection mode. But it would be a stupid circuit if it shuts down completely and identifies a full discharge as defective. A charger should be current limited and drop the voltage (with the current dropping as a function of voltage with the cell charging characteristics) when strongly discharged. It is pretty bad engineering if (some?) brands of chargers are refusing to work at their max charge rate from a fully discharged state. It makes me wonder if they just want packs thrown out under circumstances where anything is atypical due to potential liability. Lithium ion batteries can be dangerous when overheated etc and you could do that at a prolonged high charge rate with a damaged cell. Care is certainly in order when tinkering with battery packs. The stored energy can be substantial. Some of the stuff you see online with people claiming to "jump start" dead batteries with short to burn out bad zones seem imprudent at best and as you point out could get wildly different results depending on the nature of the issue and small details of how you jumper things etc. But conversely, if you can identify a bad cell and replace it using reasonable care with the right tools (soldering skills etc), I do not see why it should be so problematic. Of course the manufacturers will tell you not to do that since they do not want to be blamed with anything stupid done and they would rather sell replacements and have you throw a full pack away.

Taking a look at my pics above, how would you recommend identifying a bad cell?

 

[kbeefy]

I have a 12v battery that does the same thing, one day it would only illuminate one bar on the power meter and wouldn't charge any higher.

I finally took it apart and measured the cell votages. As mentioned previously, I found one cell with very low voltage and the others fine.
I happen to have a 3v charger for flashlight batteries so I used some jumper wires to charge just that one cell.

It took a charge, then I reassembled and put it on the tool charger. It appeared to charge up fine, I got 3 bars again and thought all was good. When it had been used a bit I put it back on the charger and the original problem had returned.

I haven't opened it back up to confirm, but I assume the same issue has returned.

 

[lund]

A lithium ion cell is considered fully discharged at around 2.7 volts per cell, and fully charged at around 4.2 volts per cell. The low voltage cutoff curcuit in either the tool or the battery (depending on brand) will typically stop the tool from discharging below that point. However, if a battery does get discharged below that point (self discharging from sitting for a long time, used in tools that don't have a low voltage cutoff circuit, etc.) the charger will recognize that as a trouble state and will not charge.

That's why "jump starting" batteries is a thing. You can charge a battery up just enough from connecting it to another battery with a higher charge state that you can bring it back above the threshold where the charger will charge it again.

Thanks.

It is a peculiar choice of "protection" mode to have chargers incompatible with full discharge states. From what you say, my charger must not have had protection in it since I had no issue charging mine from full discharge. However, it would be "easy" (if you have something to do it) to connect a discharged battery pack and/or cells to an energy source (another battery, power supply, etc) to bring it up above threshold to work with a low threshold limited charger. But that should be done with some care not to let currents become too large. You could put a limited resistor (in series) with the battery and power supply and let it take a while to bring above threshold. But if there is a bad cell wired in the pack, that might cause issues depending on the nature of the fault.

I can see why the manufacturers might low threshold limit chargers since the cells store a lot of energy and they want to reduce risk. So in any sign of problem, they probably want the consumer to trash/recycle them vs risk overdrive. Also, most type batteries (including Lithium ion) last longer when not fully discharged in many charge/discharge cycles. So having the tool stop at above low discharge threshold makes sense for longer life. But I doubt charging once from full discharge is a big issue. That had to also happen in manufacturing

 

[MOS3522]

You are missing a golden opportunity. Take that dead battery to the gun range and put a rifle round through it. The fire will be impressive.

 

[lund]

Taking a look at my pics above, how would you recommend identifying a bad cell?

Sorry, I did not register this earlier.

I am not sure. Generally, it would be easiest if you could remove the individual cells from an assembly and then test each cell and try to recharge them individually (connect to a power source and slowly increase voltage till they are to design voltage ... be careful not to over voltage them too). If a cell does not charge, it will be bad and can be replaced (find similar spec cell). Also let charged cells sit and see if they discharge appreciably (if so they have internal damage and should probably be replaced). You will also want to discharge all cells on the bench before reassembling and may need special provision for initial charging from full discharge according to what some have said here. Soldering cells without leads can be difficult since you need care to not overheat the end cap connections and damage the cell.

It would probably be ok if you measure one dead cell (little voltage across it) to just remove and replace that one cell. But be careful soldering on anything charged! I would discharge all cells first to be safe.

In your case, you have a "flexvolt" battery and I presume a circuit must be altering series/parallel cell connections between charge and discharge mode and/or DC to DC converting (more complicated if so?) output somehow. I am not sure if that would make bad cells easier or harder to extract, test, and reassemble.

Hope this helps. Just be careful with charged batteries and suspect cells. They can store a lot of energy and some people online are very cavalier about shorting terminals etc. I used to work on electronic equipment and both batteries and large (electrolytic) capacitors can be scary. I sometimes think we have gone crazy packing so many large battery cells in homes (EV/hybrid in garage, solar battery packs, laptops etc etc). What could go wrong ... most are made in China ... ha! Even larger tool batteries should be treated with some care when stored and recharging. Cells going bad mean others in the pack may be too.

 

[HyperPete]

 

[RTM]

I would watch carefully how the statistics of garage fires evolve as more electric cars fill garages

Wait a minute. Who can actually park their car in the garage? I've been in my house 20 years, and the car was inside for less than a week, very early on.

 

[lund]

Wait a minute. Who can actually park their car in the garage? I've been in my house 20 years, and the car was inside for less than a week, very early on.

I see you are in the SF bay area though with mild winters etc. Those of us in the with colder winters for sure use the garage more whether the car is gas or electric due to snow/ice/condensation etc.

Also, for an electric or plug in hybrid, you want the vehicle relatively close to the large charge station to shorten leads to connect to the charger. This will result in more people, even in milder climates, putting their cars in garage unless they make outdoor charging stations (inviting other weatherizing problems).

I suspect that electric vehicles will result in more time spent in garages that are usually attached to the main house with more potential for fire issues etc.