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Flat battery

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Bob Lamb10/03/2012 16:32:37
121 forum posts
34 photos

I have a Bosch GBH 24 VR SDS cordless drill which was great when it worked esp drilling concrete. Unfortunately the battery is now no good and a replacement was well over £100 and I suspect the old fitting would mean I would have to get an old technology battery if I could find one.

I asked a friend whether it would be possible to get a transformer to run the 24 volt drill off the mains and he did a lot of umming and aaahing and said it probably wasn't worth it - mumbling about sizes of transformers and other things I don't understand. My question is does anyone think there is a relatively easy solution to get it working again from the mains and if it is a difficult problem does anyone want the drill for themselves to try and get it going again. I'm in north London if there is no easy solution and you want to have a go - as someone used to say...........

I know it's not strictly model engineering but you could always use it to put up shelves in the workshop!


Keith Long10/03/2012 16:49:17
802 forum posts
10 photos


If you can get the old battery case apart then you'll find that whats inside are pretty standard NiCad (might be NiMh if newer) cells simply wired up to give you the voltage, and the chances are they'll be of Far East origin as well. It's perfectly possible to buy the cells and rebuild the pack yourself at a heck of lot less that Bosch will charge you for a replacement battery. I've done this myself with Wickes cordless drill. The other advantage of doing this is that technology has moved on and you're not restricted to the same capacity as the duff unit. High capacity cells are aailable for very reasonable cost and are the same size. In my case I fitted 3600 mAhr cells into the case that had originally contained 1200mAhr units. The result is that the drill needs charging once a day instaed of every 2-3 hours when I'm giving it some stick - and the same charger works as well - just takes longer.

If you don't fancy the DIY approach do a search with Google or similar, there are a number of companied around selling pattern batteries for the Bosch power tools. I bought one for a hedge trimmer and it works just fine, and was quite a bit cheaper than Bosch wanted.

I'd definitely have a go at this rather than wind up with the drill hung on a cable - you might just as well use a mains unit that'll have more grunt.


Bazyle10/03/2012 16:58:20
4895 forum posts
195 photos

24 v right? While you could make up a battery pack from individual batteries it might be more trouble than you want t get it all into the space.

A mains supply might have to be a bit big to supply the current  however if you are looking at CNC then 24v seems to be popular and it might do double duty.

However there is a nice size of lead acid battery 6V 4.5Ah that is popular in model boating circles so it is relatively easily obtainable at acceptable prices. Make a belt that takes 4 of them in pockets with each battery on a plug/socket and a flying lead and it is still portable. You can use the batteries in your model boat (go on make one). Remember lead acids MUST be given a charge every week.

Edited By Bazyle on 10/03/2012 16:59:16

Bob Lamb10/03/2012 17:21:42
121 forum posts
34 photos

Thanks for those ideas - I had become fixed on the idea of connecting it up to a mains lead somehow - it's always good to get another (better) mind to the problem. I like the idea of keeping it portable.


Richard Parsons10/03/2012 17:44:46
645 forum posts
33 photos

There was way back when a series in the Model Engineer which showed you how to build your own NICAD battery reconditioner. I did not build one as I had such a thing included in my Video camera. NICADS seem to 'form a memory' of its charge/discharge cycles. What the thing did was a series of charge-discharge cycles. But as good things go they both went. The camera was broken when someone knocked it out of her hands and she would not use the lanyard. The charger was lost when a Hungarian left it out in a thunderstorm. he forgot it or did not want to get his 'T' shirt damp.

Have a look for the thing if you know where the ME indexes are



Gone Away10/03/2012 18:49:30
829 forum posts
1 photos

Dick, when you rebuilt yours, how did you make the inter-cell connections? All the battery packs I've seen have spot-welded strips to make the connections between the individual cells. I tried soft soldering some but it wasn't greatly successful.

Bob, another idea along the same lines is to check around (internet, yellow-pages, CraigsList ?) and see if any local tool dealer offers a power-pack rebuilding service. For example I have a (fairly) local tool store that sells mostly cheap imported tools plus some top brands and the gent there will rebuild your pack with new nicad cells - or sell you the cells if you want to do it yourself. I believe he spot welds them. He charges for the cells plus a labour charge which is actually quite reasonable.

Keith Long10/03/2012 19:11:25
802 forum posts
10 photos

Hi Sid

I think you meant to aim your question at me rather than Dick.

When I bought the cells to rebuild the battery for the drill, I got the type that have "solder tags". In practice the "tags" are strips of metal that could fold over the battery length ways and nearly touch - but they stop just clear of each other. So they are much bigger than what I used to know as "solder tags", but you can soft solder these quite easily to make up the pack. If you need to get them to a funny angle then fold them over with a pair of pliers and flatten them well down. To extend the reach of the tag then a bit of - ideally- copper shim would suit or a bit of brass. The main thing I found was that they have to be packed together very tighly to go back into the battery housing. It's better to work on that aspect first and then sort out the interconnections afterwards, but all quite do-able on the kitchen table, you don't need an electrical workshop.


Clive Hartland10/03/2012 19:11:43
2501 forum posts
40 photos

The replacement of cells in a battery is simple, we do it almost every day at work. Regarding the connecting straps, all we do is solder them on. We do not let the soldering iron dwell on the battery too long.

There is a Company called, 'All batteries'. they do re-celling and it might be worth asking them.

They are the people we buy our single cells off to make up our own packs.

If you do it yourself it only needs the casing cutting open and you can do this with one of those 'Razor' saws. Photograph the interior and proceed as per Kieth.

I would definately have a go.



Edited By Clive Hartland on 10/03/2012 19:20:23

RJW10/03/2012 20:43:38
340 forum posts
48 photos

I zapped a few of my totally dead 'Performance Power' (B&Q) 18V batteries with an arc welder, and another time a fully charged car battery and heavy jump leads, worked a treat!

They didn't explode, but got pretty hot mind, and once allowed to cool they recharged like good-uns!!

If you Google 'reviving dead ni-cad batteries' or similar, you'll come up with more hits and U-Tube videos than you can trawl in a lifetime!

You may have totally dud cells in the pack, in which case the routine won't work, but you've lost nothing if it doesn't, and gained a working power tool again if it does, 3 out of 4 of mine got revived, and the one that didn't got new cells cheap courtesy of battery packs bought off eBay, which I split down.


Ady110/03/2012 23:23:18
3503 forum posts
513 photos

Nimh seem to be the biz.

I've got an ancient mobile phone and an old black and decker Quattro unit with NiMH batteries.

Both are fine and still recharge no problem

NiMH seem to go on forever.

Terryd11/03/2012 05:50:56
1926 forum posts
179 photos

Hi Bob,

I did the same as Keith, opened up the battery pack and replaced just one leaking cel. the whole thing worked well for a long time afterwards. It's not rocket science and soldering is easy and works perfectly.



Richard Parsons11/03/2012 08:44:12
645 forum posts
33 photos

Clive what solder and flux do you use. I have tried that trick several times and have had problems soldering in the new cells. Originally they were spot welded.



Francis Sykes11/03/2012 09:03:58
43 forum posts
5 photos
I used to solder these packs up in my radio controlled cars days. The cells used are almost exclusively sub C size, the best way to solder them is with multicore soft solder and a relatively large soldering iron, as said before, with minimal time on the cell. I use a 40 watt Weller, commonly available.

Good luck with your fix!
Mike11/03/2012 09:10:15
713 forum posts
6 photos

Bob: If you haven't found it already, there's some useful stuff at

John Shepherd11/03/2012 09:13:56
216 forum posts
7 photos

Slightly off topic, but re soldering connecting wires directly onto cells is not good practice and DO NOT do it on Lithium cells unless they have tags and even then make sure you are quick.

The results can be explosive and I can assure you that the amount of energy and toxic smoke released from even an AA size cell is amazing and could easily put you and your workshop out of action!

This does not apply to the rechargeable Lithium Ion cells that might be found in drill batteries but still take care not to overheat the cell which can easily happen if they don't have tags. (connecting tags are spot welded on for a reason which is not just related to cost).

Another thing to watch out for is that some batteries have thermistors and diodes built in for protection, make sure these are retained if replacing cells.

John Shepherd

Clive Hartland11/03/2012 09:48:58
2501 forum posts
40 photos

Dick, hello, I always brush the batteries with a steel brush and the tags if any and just use ordinary flux and lead/tin solder. maybe the tales of woe about battery soldering are with the new type solder?

We make up 7Ah batteries for powering theodolites and lasers underground so we have other criteria to adhere to as well.


Ian S C11/03/2012 11:11:00
7468 forum posts
230 photos

In Christchurch (NZ) we have a battery shop who will reload battery packs for about half the price of a new pack, and at least double the Ahr rating. Last one I had done was my ancient cell phone, before that, a hedge cutter, and a cam corder.

You can get a bit more life from a battery if you put the battery in the freezer for 12hrs, take it out and leave it for 12 hrs then recharge. Another way is to zap each cell with a charged up electrolitic capacitor, that involves breaking open the battery pack. This last method burns off small filaments of nickle that short out the battery internally. Ian S C

Clive Hartland11/03/2012 11:28:26
2501 forum posts
40 photos

I think the little whiskers are called, 'Dendrites' Ian and are the main failure of an NC battery.

Zapping the battery in the reverse polarity I beleive is the way to burn them off.

Another factor about NC batteries is that the are Finite life, that is they have about 500 charge and discharge cycles before they fail.

They should be charged from a depleted condition of 1.1 Volts per cell for the correct time of 10 xC.

The practice of topping up a charge is fatal to them and is the cause of the memory condition, this can be got over by a full discharge and re-charge 3 or 4 times to rejuvenate them.

The NiMi batteries are different and do not have memory problems.

Storage is another problem with advocates of a full charge and others that they be stored in a depleted condition.


Russell Eberhardt11/03/2012 15:57:36
2533 forum posts
85 photos
Posted by Clive Hartland on 11/03/2012 11:28:26:

Storage is another problem with advocates of a full charge and others that they be stored in a depleted condition.

It doesn't matter whether I store them charged or not. When I come to use them the damn things are always flat!


Clive Hartland11/03/2012 17:57:07
2501 forum posts
40 photos

Maybe because they have a resistor in them that leaks the chage slowly, my battery drill does the same and in two hours is back up again.


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