How To Fix A Flexvolt (not jump-start)

I received this 9ah flexvolt battery which was in a sub optimal condition upon inspection the voltage was low 2v in the 18v/ 20v range and 6v in the 54v/ 60v range. The issue with the battery was the voltage it was much to low for the charger to be able to charge it so I had 2 options. The first option was to attempt to jump start or boost the battery by connecting it to a good one. I choose option 2 which was to raise the voltage slower over about 5 hours in fact using a DC power supply. The method is as follows connect the power supply until the voltage reaches around 17v this should bring it into charger range then connect it to the charger if there are no other internal issues the charger will then charge the battery fully. I must say it worked a treat the battery recovered completely from its low voltage state it doesn't always work but it did this time.
How to test voltage on a Flexvolt is shown here too.
Dewalt Flexvolt battery won't charge on the Dewalt charger? This may be of help
the items used in this repair
Venlab Digital Multimeter
UK amzn.to/3KDi805
USA amzn.to/3MlEep8
DC power supplies
UK link amzn.to/3LMSO93
USA link amzn.to/42ya87A
The flexvolt battery is a dual voltage innovation from dewalt it is suitable for 18v and 54v tools 20v and 60v in USA. The 9ah flexvolt uses samsung 21700 cells as opposed to the 18650 cells used by the 6ah flexvolt and XR. I show how you can sometimes repair these by relatively low cost means. Can You repair your 54v/60v flexvolt battery if its not charging ? If I can you can
#repair #dewalt #powertools

[@doctorlefthandthread]

The items used in this repair Venlab Digital Multimeter UK amzn.to/3KDi805 USA amzn.to/3MlEep8 DC power supplies UK link amzn.to/3LMSO93 USA link amzn.to/42ya87A

[@Haggis20012]

What unit did you buy? 30v 5ah or higher?

[@yousefalmarhoon8789]

Have the same problem with Milwaukee 8.0ah battery which charge only 3 bars without completing the 4th and have a 12 ah with no charge as well, opened it and checked the cells 3 of them was 3.8 and others are 4, I need to find a way to balance them now, which I am gonna try, this coming weekend 🙂

[@doctorlefthandthread]

Makes sense they are out of balance

[@UCs6ktlulE5BEeb3vBBOu6DQ]

Careful with that, I just diagnosed such a battery for someone and one cell was at 5.3v and another was 0.3v. That 5.3v cell is a pending home insurance claim. A cell under 2v can't be recovered, it has to be replaced.

[@doctorlefthandthread]

5.3v wow yeah that's high

[@mrclive5]

Had a 6 Amp Flexvolt refuse to charge today. So I stuck it on a heat gun and ran it until the heat gun stopped. Then the battery charged! Happy days!

[@doctorlefthandthread]

Works sometimes

[@nicevideomancanada]

I'll have to try that if I had a heat gun. My 9AH won't charge. I watched this video that explains what the main problem is: kzbin.info/www/bejne/kHurfKKlZ9ibeKMsi=scqrbh1N1hQQ_HsU

[@hugobose2254]

a great Vid, I thought that you needed a dcb118 charger to charge 9ah batteries?

[@doctorlefthandthread]

Any 18v/20v dewalt charger charges a flexvolt it will charge quicker on the dcb118 than the one shown here. Flexvolt don't charge at 54v/60v they charge at 18v/20v.

[@hugobose2254]

@@doctorlefthandthread I thought that But me asking Will help others in the future whit the same question

[@doctorlefthandthread]

It Sure will thanks for all your comments and questions.

[@jpmkiv]

Had this same thing happen on that same 9ah pack. I charged it using a hobby charger at various cell count settings..

[@nicevideomancanada]

could you design and produce a Jump-start charger product for sale.

[@doctorlefthandthread]

The jump Start is frowned upon by some due to the sometimes volatile nature if lithium ion however you can use a dc power supply to bring one of these batteries up slowly

[@segovia102]

Have a 9ah that reads 17v between b terminals. Almost never used, charged less than 10 times. Was able to run a Dewalt chainsaw with what was left in it but will not take a charge now. Any ideas? Charger is working on another 9ah. Will charging with a desktop power supply balance the cells if thats the issue?

[@doctorlefthandthread]

Sometimes running it down to a very low voltage then bring it up with a desktop power supply can work. It has for me but it doesn't always work.

[@stevensondrake]

I've heard jumping these batteries can turn them.into a fire hazard. Is that true? If you have a dead cell it over charges the other cells

[@doctorlefthandthread]

The cells have a little failsafe on them that breaks the internal connection rendering the cell useless if it gets over heated of overloaded. The failsafe is more likely to deactivate the cell. If the cell doesn't deactivate you can experience something called thermal runaway where a cell keep heating up until it explodes. This is very rare and I have never experienced it yet but it is highly dangerous.

[@grantmacdonald3126]

I have an issue with a 9ah flex volt, goes on charge, but stops charging after 5 mins, only one led bar lit on indicator, but charger says its full. Got 16.5vdc across B+/- terminals, can this be saved?

[@doctorlefthandthread]

Possibly try this first kzbin.info/www/bejne/f4bPeYmMqZKjqsk

[@grantmacdonald3126]

@doctorlefthandthread everything is intact, no burnt or broken connections. I used a jumper across C connections and pushed plungers, got 49.7v on the 54v side. Digging a little further I think I have a dead cell. One is reading 0v, with all others giving 3.4 to 4.0v

[@doctorlefthandthread]

@@grantmacdonald3126 hard to change a cell in the flexvolt

[@patryksyrzan6666]

Hi there I have a problem with my DeWalt 6ah as soon as I put it in the charger the light comes on and then off straight away. Any idea what could it be ? There's no breaks in the nickel contact bars.

[@doctorlefthandthread]

Could be dead cells or something else popped on the board

[@patryksyrzan6666]

@@doctorlefthandthread my 9ah had some visible bits of coating missing from the board and it only charges one bar

[@theobiolley7610]

Thanks for this videos, i got the same 9ah flexvolt. But my problem is that it doesn't charge over one bar. Do you think jumpstart would work or some cells my be dead? Thanks for your help❤

[@doctorlefthandthread]

Good question and I managed to get one going that had the very same issue I used a USB adapter on a ring light to drain the battery down low then brought it up using the power supply as shown in the video to around 17v it then took a charge

[@gonerydin4225]

Dewalt will replace defective batteries

[@doctorlefthandthread]

In USA yes not UK or Ireland sadly one year warranty except powerstack where you get 3 years if registered

[@konstantine381]

I thought that being 6 volts across the pack would mean it's dead as a doornail. I got a 12ah here with water damage and it's reading 0 on most cells. I doubt this would work for me

[@doctorlefthandthread]

Probably not. sometimes if there is some kind of voltage you have a chance to bring it back. conventional wisdom would dictate that if they are below 3v volts I am not conventional or wise so sometimes it works for me

[@konstantine381]

​@@doctorlefthandthread got a 6ah, its a 2022 battery in great condition. Wont charge but voltage across the pack reads 14 something volts, would ya say its fixable?

[@doctorlefthandthread]

@@konstantine381 it could be check for broken connections kzbin.info/www/bejne/mnWzYoZ-nbGagpY

[@konstantine381]

@@doctorlefthandthread no broken connections, looks like someone's resoldered the board on but the battery works in 18v and 60v. It just has a solid light on the charger and the cells are all 3.3v after i jumped them but still no luck. Might see about replacing the board

[@doctorlefthandthread]

@@konstantine381 what voltage do you have at the 60v range?

[@raljame]

Why did you test it on an 18 volt tool and not a 54 volt tool?????

[@doctorlefthandthread]

Thank you for commenting yes you are correct the right thing to do is test it on a 54v tool. So why didn't I? The simple answer is I did not have a 54v tool available that day but it did work on 54v. I did get it tested later.

[@drumnagranshy]

Cheers 🎉

[@AKZL76]

Had a flexvolt saw burn out on me and the 54v battery that was in the saw only works in 18v tools now is there a way of fixing that? Maybe its stuck in 18v? Any ideas? (Tried another 54v battery in the saw and that too only works in 18v tools)

[@ianhelsbyservices]

You suggest the second battery only works at 18v too. Did it work on 54V before? As if trying it in the burnt saw broke the second battery? have you tried the shorting of C1 to C3 and measuring output voltage?

[@AKZL76]

@@ianhelsbyservices yeah both 54v flexvolt batteries where working before on 54v now after been in the burnt out saw both only work on 18v tools. I'll try short the c1 toc3 when I get home Thanks for replying

[@doctorlefthandthread]

Try this too kzbin.info/www/bejne/aKW3iWp6f96qn8k

[@ianhelsbyservices]

I've been given two 9AHr batteries to diagnose. Charge and work fine on 18V but no 54V tool to test. Tried the jumper between C1 and C3 but no change. Output is 20v then when you press the side buttons it graduslly drops to 0v as if output disconnected and capacitor discharging. Any ideas?

[@doctorlefthandthread]

There may be a burnt out connection I would guess this might help kzbin.info/www/bejne/aKW3iWp6f96qn8k

[@ianhelsbyservices]

​@@doctorlefthandthreadi must apologise. Turns out I hadn't pushed the side plungers in far enough. Half way in drops the voltage to 0v over time. All the way in so you can't see the black plunger any more gives just over 60v. Batteries all check out, must've been the dirty contacts!

[@Ben-xd4fc]

Thats how it should be done nice one. BTW the 6Ah flex uses 18650s

[@doctorlefthandthread]

It does thanks for your advice regarding that I am getting there

[@garthqueen]

So did the older 9ah apparently.The ones with the silver tabs on top had the upgraded cells.Ive got both.(vs 21700 cells)

[@thehhoff69]

@@garthqueen The older 9Ah (mid 2018 and prior) used Sanyo 20700 cells, not 18650s.

[@blamsing]

This method worked for my battery that showed 1 bar only but would never charge past it on the dewalt charger. I slow charged it for 3-4 hours and it came back to like. I spent $30 on a dc battery charger from amazon to save a $180 dewault battery. Well worth it. Thanks for making this video!

[@doctorlefthandthread]

Great to hear