Cordless drill replacement battery ??

[wombat]

Hi Guys
First time here .. just a virgin !!
I am going to try to replace some dead cells in my 12v cordless drill. I have identified 4 that are dud with the meter. I know that they are 1.2v sub c 1200 mAh but find that these are hard to find.

I have found 1.2v 1600 mAh and my question is will it make much difference if I use 1600 mAh instead of 1200.. I am not worred about blowing up the drill .. it is just my face that I am worried about.

Any help appreciated
Regards
Michael

 

[(*steve*)]

1600 Vs 1200 is not a problem. But replace all the cells, not just a few.

 

[wombat]

Thank you for your prompt reply. The other cells seem to be ok at 1.2v.

Is the reason you say replace them all because I will know that they are all brand new or is there some other conflict with mixing the 1600 vs 1200 ??


Regards
Michael

 

[(*steve*)]

The main reason is that you want all the batteries to have as close to the same capacity as possible.

Capacity decreases over time, so even if you had 1600mAh batteries in there, replacing a few with new 1600mAh batteries would mean some had higher capacity than others.

The other issue (and it's related) is that the batteries may be in different states of charge.

The problem boils down to the fact that if one cell gets charged fully, either you have to stop charging there, or continue, overcharging this cell (and damaging it) whilst charging the others. During discharge the reverse happens with one cell discharging before the others do. This results in an over discharge, and possible reverse charging -- which is also very bad for the cell.

The practical upshot is that the cell with the lowest capacity often goes between over charge to over discharge, losing some of its capacity each time, thus making the process worse and accelerating the eventual demise of the cell.

Replacing some cells leads to the more rapid degradation of the others. If you then replace the failed ones, the older "new" cells are in the same situation and have a shortened life.

Be nice to your battery and replace all the cells at once with exactly the same cells (preferably all individually charges (or discharged) to the same point).

Do this and you'll only have to do it once.

 

[wombat]

Thanks again Steve
Just one more silly question (you can see that I am not an electronics buff !!)
If I change them all and use say 1600 or 2200 or even 6000 mAh will that harm the drill or just give me extra staying power (so to speak !!)
Regards
Michael

 

[(*steve*)]

Changing to a higher capacity cell should just result in longer charge times and longer life between charges. It should do no harm.

 

[Tesla]

I've done it before, but to tell you the truth, it's not really worth the money saved due to the time it takes ... especially if you have to solder the individual cells themselves.

I fixed a B&D 18v Firestorm battery with a battery from Harbor Freight. Just had to switch the cases and main wires. Saved $20 and it works.

I have new Milwaukee Lithium tool set now, but even though the B&D set was 15 years old, I hate to trash them just because the NiCd batteries wore out. So now, I can still use all those tools again. I keep them in the workshop and the good set is in the garage.

If you want to use original charger, battery cells should be pretty close to original (same chemistry, etc.) although, you can increase total amps a bit without a problem.

 

[(*steve*)]

just because the NiCd batteries whore out.

Wow, is that what happens after I loose them?