replacement batteries

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MB Enthusiast
Sep 27, 2007
Audi A4, 1994 E320 Coupe, 1995 E300 estate
My small drill is a dewalt DW907. one of the battery packs (code DE9074) is not holding charge so I open it up and find 9 batteries linked together (again, not unsurprisingly). If I go to Maplins can i

1) buy either replacement batteries for me to link together (and uprate the amp hours from the current 1.3 to say 3) or
2) buy ready made replacement "packs that just need to solder to the original connector?

Not that urgent as i dont use the drill that much so i can make do with the one battery that works fine currently (sorry about pun) and I cannot be bothered to pay £20/30 for a new one.
I'm having exactly the same problem with ' Old Faithful' my DeWalt 927 , it uses the same batteries as yours , 9074's and one just wont hold a charge....

Me being tight won't buy a new battery and currently make sure each job is finished before the one working one runs out ( although i have been caught out a couple of times !! :eek: )

I'd be interested to see what options for fixing it on the cheap are available as well ..
yes you can remake battery packs as you can see for yourself, thats all they are and if you can get a higher rating then it will last longer on its charge, if they are `C` size cells I would recommeded a radio control car model shop as they will sell very advanced batteries which will allow very high discharge rates and high charge cycling, they will also be able to supply everything you need to make the battery pack, ie, all the copper bus bars to link them together, I myself made a new battery pack for an old Ericsson phone years back which I gave to my father, its still working,
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If you decide to do it yourself, under no circumstance use non-rechargeable batteries in the pack and then try to charge - this could lead to an explosion. I'm sure you knew this, but I have actually come across someone trying to do exactly that. :crazy:

The other thing to be careful about is to get rechargeable batteries suitable for the charger you're using. Not all battery technology is the same and chargers must supply a charging current and circuitry that matches the batteries' requirements, otherwise you can severely reduce their useful life or damage them. Don't charge Li-Ion batteries using a charger for NiCd or NiMH for example.
You need to establish what size and type of cells the existing pack uses and then find some decent equivalents. However, there are many pitfalls along the way and you also will need to be able to solder well. Most drill packs that I've seen use sub-C cells and to buy decent types of this size, you're looking at paying £5 or more per cell. Yes, you can buy cheaper ones, because that's what was in there to start with, but they won't perform or last as well. Frankly, it's much easier, cheaper and safer to just buy a replacement pack off Fleabay, which is precisely what I did recently.
Gotta be honest , after reading all this , i'm leaning that way too :eek: :rolleyes:
me too! :eek: Howard, we are clearly both cowards! :D
In fact , i just picked one up for £15 :bannana:

Happy Happy Joy Joy ....
Fleabay or elsewhere?
Fleabay ...

Brand new :cool:

Nice ....
Yup soldering up packs is pretty specialised ... you need a very powerful iron (a lot of heat for a short time, to avoid damaging the cells), and if connecting cells inline a jig and a hammerhead ("T") bit.

As mentioned, nicd / nimh / Li Ion (and Li Fe, and Li Po) are all different technologies and need the right charger. Get it wrong and packs can explode or burn - not nice!

If you don't know exactly what you're doing it's best to stick to commercial packs.
Zapping and matching cells is fairly standard practice when making up competition nicd or nimh packs for r/c aircraft/cars/boats.

Zapping is approximately as above, but normally done with a bank of large capacitors. It can lower the internal resistance of the cell, giving better voltage under load.

Matching involves plotting a discharge curve for each loose cell individually, then assembling packs from the ones that are closest in characteristics.
Why do rechargeable cells seem to be 1.2v not 1.5v,ive a tester that takes 6*1.5v aa batteries but it wont work with rechargeables as ther only 7.2v in total not 9v
Why do rechargeable cells seem to be 1.2v not 1.5v,ive a tester that takes 6*1.5v aa batteries but it wont work with rechargeables as ther only 7.2v in total not 9v

Thats right, thats the main problem with rechargables.
Why do rechargeable cells seem to be 1.2v not 1.5v

The charge depends on the technology used, but you are right that common types of rechargeable batteries such as NiCd and NiMH AA, AAA, etc ones provide only about 1.2V.

Rechargeable alkaline batteries (do not confuse with non-rechargeable alkalines!) should be better in that respect and provide about 1.5V initially. After a few dozen charge cycles that voltage will eventually start to drop off too and so you might need to replace them again (i.e. their total useful life will be less than for competing technologies).

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