Rebuilding batter from 4xxx series

[newmom]

I have made a couple of previous attempts at battery rebuilding and then put it away when I got stumped, but now I am starting a third time. I have reviewed what I could find on this subject and it was helpful but I still have some specific questions.

I have opened up a battery which was made in 2004. It contains a NiCd battery pack with the number 2400 on it. I have 12 brand new NiCd batteries but they have a number 2200 on them. Can I use these batteries? They have a photo of a Yellow Roomba Battery on the package but I am concerned about those different numbers. I got these new batteries, unopened in a lot.

I have tested the individual cells while still all connected together on the dead battery cells. The volage readings range from .49 to .72. I also tested two of the new cells for reference which tested 1.2. The new set have the tabs on them and both sets are made by Tenergy.
I am operating from the premise that Nicd batteries do not need to be tested under load, is that correct?

Are all the cells in need of replacement, or are some of the cells good enough to use by adding the better cells. I was hoping to use the 12 new sub Cs in a few of the old batteries, but don't know how to judge those readings I got. I know after charging they need to get to 1.2 or so but I don't know if given the readings I got, that IS the voltage and I need to replace them all.
Perhaps I should have charged that very old battery before I took it apart???
Thanks for your continued expertise help.

[mfortuna]

2200 means the cells have 200 mAH (milli amp hour) less capacity which is no big deal. NICADs need to be tested under load just like NIMHs. I would not bother trying to replace a partial amount of cells in a multiple packs, use all 12 new cells to build a new pack. The voltage readings indicate all the old cells have been over-discharged. My guess is you would end up with two or more poorly performing packs if you tried to do partial replacements.

[newmom]

Thanks for your reply Mike. For future reference, should I have charged that old battery before I did the testing on the voltage?

[mfortuna]

It doesn't hurt to charge it first. You need to measure under load to get an accurate reading. The readings you got were pretty low since a properly discharged battery should show a no-load voltage of > 1V.

Also, be careful charging batteries of unknown condition in a 4xxx series because of potential damage to the FETs.

[newmom]

Again Mike, thanks very much for this information. I did not attempt to charge this battery, but when I do have old batteries, I generally use my old black external charger first to try to bring them up to a suitable level. Is that safe to do?

[newmom]

One more important question; there are two tabs on each of the new cells. My husband says we need to remove one on each end as we only need one tab to connect it to the other batteries in the new pack. I just want to be sure that is right as I can't see any remnants of a pulled off or cut off tabs at the other rebuild battery packs I have opened up to use an as example.

[vic7767]

Some of your new sub c cells with the tabs will still use both tabs. It will depend upon their position within the series lineup of your new battery construction.

[TechGuy]

The tab allows one to solder to the battery easily. It is okay as long as the negative terminal of one cell is soldered to the positive terminal of another cell. What you do with the tabs is up to you.

[newmom]

Thanks to you both. We have the battery together now and are charging; but it has dawned on me that there wasn't a thermistor in the battery packs that we used. What can I do about that? Do I need one and if so, where do I get that? We are having a lot of difficulty testing each cell under a load. We have the small lightbulb, which works when we test it on a regular size D battery, but does not light up with any of the cells. When testing the full battery with a multi meter we get 15 volts, but we can not get any of the individual cells to light the bulb. When tested on the mulitmeter, they all have over 1 volt. We have been working on this all morning, and have made some progress and like a lot of other people who have tried this, are getting a little frustrated and feel lke we are missing some important piece of the puzzle. (Well mostly my husband is getting frustrated). My only frustration is that I am afraid he is going to give up on trying to teach me how to do this.

[mfortuna]

You need a thermistor or else the roomba will not charge the pack. I use the one that was in the OEM pack.

To test the pack discharge the entire pack with an automotive bulb and quickly measure each of the cells. You should have plenty of time at first since the pack should light the bulb for an hour. Keep measuring each cell and look for the low ones. Disconnect the light if any cell gets below .9V

[newmom]

Thanks very much. I will open that battery back up and salvage a thermistor. Oh boy, will my husband be excited! Thanks once more.

[vic7767]

I also offer a thermistor and polyfuse for battery pack hackers on the website.

http://www.robot-doc.com/22.html

[newmom]

Just for clairity, can I use a thermistor from a Nihm battery on a Nicd battery pack? If so, I have a few of those but if it has to come from a nicd pack, I will have to do some more searching or buy one from Vic.

[vic7767]

You can use the thermistor from any of the Roomba packs. The battery chemistry does not matter.

[newmom]

You can use the thermistor from any of the Roomba packs. The battery chemistry does not matter.

Big help, thanks. My husband says these are spot welded onto the cells and not soldered? We are not sure how to remove them from the old cells in order to solder them to the new cells. Once we finally get this one finished, we are hanging up our battery rebuilding business. My husband doesn't have the patience, (nor an entire Sunday) to spare

[vic7767]

I use a pair of needle nose pliers to pry up the tacked on strips. Then you might save enough of the strip to re-solder onto a battery contact. Of course you don't have to, you can just use some insulated wire.

[newmom]

That's what we needed to know. Thanks very much.

[mfortuna]

It might be better to strip off all the insulation if the wire is too thick to allow the case to go back together.

[newmom]

Thanks Mike, We got the case back together now we will see if it will charge.

[newmom]

It has been running the Dirt Dog for over an hour now, so guess we are good to go. Thanks to all who offered information.