Instructables

IRobot Dead Battery Cell Fix

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A step-by-step tutorial showing how I repaired my $60 Dirt Dog battery with just a AA battery and some tape. We start off with a Dirt Dog battery that has a voltage of 15.87V which is indicative of a bad cell. When we complete the repair we are at 17.12V and that is without even charging the pack.
 
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Step 1: Remove Triangle Screws

Picture of Remove Triangle Screws
The iRobot battery has a bunch of annoying triangle shapped screws. I've read that some people can easily unscrew them with a appropriately sized flat had screwdriver. I used another technique which works for most "secure" screws types.

Step 2: Dremmel the Screws

Picture of Dremmel the Screws
I used my dremmel to cut flat lines across the screws. Later I cut a second set (not shown) so that a phillips head can be used to unscrew and rescrew these. This is a cute trick to use for all sorts of stuff you are not supposed to service yourself.

Step 3: Get That Case Open

Picture of Get That Case Open
There are claims that you can just pop the battery lid after removing clips and doing some prying on the irobot batteries. I think there is a little more to this. The Dirt Dog in particular seemed to have a well glued on battery lid. It was no match for a dremmel. Be careful to not cut deep. Good ventilation is useful here as the plastic smells terrible when you are cutting/burning it off with the dremmel.

Step 4: The Battery Cells

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Here are the cells. These are 12 sub-c sized / 1.2V / 2600mAh / NiMH batteries. These vary between different models so yours might be a little different. The dirt dog seems to have a cheap ass NiMH (low amp hour) versus the higher end models.

Step 5: Make a Mess

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Yeah, now this is a good time. Go ahead and rip off that glue on paper stuff. It's cool. We need access on both sides to the batteries so we can find our dead cell.
Stan1y6 months ago
In the UK screwfix do a security bit set for £5 which copes with most of the common 'tamper proof' screws
Ryanmatt101 year ago
When replacing a new battery cell do you have to solder it to the other batteries or is there another way around this? Would I be able to just use the metal connector bridge and apply tape and firm pressure to make sure there is contact between the battery and the bridge, or maybe even foil?
I am having difficulty with this method. I have 3 Rombas that test good using the one new 14.4 volt battery that I purchased. When charged it reads 15.4 volts.
The other two read 18.2 and 16.5 but will not run a Romba.
I opened the 16.5 one using the chisel method (I have a triangle screwdriver). I used the dremel tool to grind a hole in the insulation and measured the voltage of each cell.
1.38 1.39 1.39 1.39 1.39 1.30 1.38 1.39 1.36 1.39 1.38 1.36 1.34
This addes up to 16.5 . This battery will not run a romba so how do I know which is the bad cell and why wont it run? (since this voltage is higher than the new one)
All suggestions will be appricated.
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I'm having the same problem, voltage measures OK but will not run a Roomba. So how did you end up identifying the bad cells?
dedson12 years ago
Thanks for the advice. I opened up my battery and found 4 dead cells. I replaced them with some spare cells I had laying around from a craftsman cordless drill. Now, instead of running for 20 sec it just ran a 40 min cycle.
Please read and reply to my post just after yours. My question is: How can I identify the cell or cells that are dead? You assistance will be appreciated.

I opened the 16.5 volt battery using the chisel method (I have a triangle screwdriver). I used the dremel tool to grind a hole in the insulation and measured the voltage of each cell.
1.38 1.39 1.39 1.39 1.39 1.30 1.38 1.39 1.36 1.39 1.38 1.36 1.34
although it is 16.5 volts is won't charge up enough to run a romba.
I solved my own problem. Once I used a battery tester and not a voltmeter I located 4 dead cells. The battery tester checks voltage under a load. They sell them at Radio Shack. You could probably do the same thing by loading the cell with a resistor while checking the voltage (or flashlight bulb.)
Sorry to tell you, but from those battery readings, it is not not the battery. The four that I found dead had readings of 0.2 and such. and then once I replaced them my battery reading was back up to a total of 16 volts where as before it was 10 volts. it might be the actual roomba that has a charging issue. Sorry dude.
How can I identify the dead cell(s). All my cells have close to the same voltage but will not charge.
sklarm (author)  POKERPOP19372 years ago
Dead cells read 0V.

If it is not charging there is probably too much built up resistance (sulfation). In that case it is typically the charger shutting off. I've made some chargers that just rev up the voltage so that weak cells can be recovered. However, they are not for commercial sale at this time.
lifes2 years ago
How can you test the cells without disconnecting them 1st???
Thanks, great idea!
sevony3 years ago
OK, a regular Torx T7 bit will work, but:

1. you have to keep firm downward pressure to keep it from walking out
2. you may damage one of the wings of the bit
3. the screws that have cracking plastic around them are torqued the most
Thanks for the irobot battery fix. Now how about that scooba battery.
If I can get in it I can fix it. Where should I make the cut?
dcr1942@GMAIL.COM
kargoe3 years ago
This is so awesome - thank you for this! I'm going to try this tonight and check the cells and drop in a few of the extra AA's I have. Is it possible, if needed, to replace ALL the cells with rechargeable AA's over time?
odikmen3 years ago
Just tried the "chisel method" and I think it is easy and not messy like a dremel disc.
belcat4 years ago
Wow.. they call that a C cell? I've seen some sub-C cells from OnlyBatteries.com that hold 4500.. they are more expensive thna their 3300mAh, but well under $100 they want for new pack. You can get AA cells that hold 2600 mAh fairly easily too, cheaper, but they may not meet Roomba's current requirements (probably do though.. if it's supposed to last 2 hours in 2600mAh, well, my camera does that too, on AA NiMH cells). You can get 6pack AA cell holders, so the next battery swap will be a easy. Tenergy also sells some nice cells.
Just tried the Chisel method and it worked great! and no mess! I just taped it where the screws go in all around and it came off very easily! Thanks 2mcleods!
torval4 years ago
 I was able to remove the triangle screws with a torx T-7 screwdriver.  
2mcleods4 years ago
 Instead of a dremel, I used a chisel with a good firm whack and it poped the case open.  3-4 whacks on each side and a couple on the ends did the trick. 
archismart4 years ago
Just go to the local hardware store and purchase a tri-wing bit - $1.99 - to unscrew case. Don't use it in a power drill, use a hexhead screwdriver or other hand tool and add a little pressure. It worked for me. Gone!
aususer4 years ago
You can open the case without using a dremmel to butcher it - or buying one of those screwdrivers from ebay:

You will need:
1. Largish (disposible) hex head screwdriver (or one of those "quick replacement" bits you always find at the bottom of your toolbox) or an old allenkey. The hexbit are the ones that have 6 sides on them.. I used one I found in my batterydrill set.
2. Angle Grinder with a cutting disk (the finer the better)
3. wide, sharp Chisel

With the anglegrinder grind off three opposite points of the hexhead driver to make a triangle. Grind and check until it fits in the screw (you can, of course use anything and grind it into a triangle - this is what worked for me)
.
Once you have the size correct, you should be able to easily remove all of the screws (and be able to put them back!).

Check to see if the case opens. Some people have reported that the case is heavily glued - others have been able to open theirs straight up.. I guess its something of the manuf. batch.

anyway... to open mine, I got a sharp chisle and a GENTLE tap on it (with my hand) and it was enough to break the glue seal.. repeat around the case.
It goes without saying.. don't be forceful or you will damage the case and batteries,. Take your time.

Using a sharp chisle and you won't get those ugly "screwdriver twists" others get trying to force the case open.

Once I did this - my batterybox looked almost new! A small cleanup of the plastic and the old glue  with a sharp knife and you wouldn't know it had been opened! 
codongolev4 years ago
 is this yours?

www.flickr.com/photos/11461247@N02/sets/72157609502196354/

because if it isn't, this might be plagiarism.
sklarm (author)  codongolev4 years ago
 woah, got some free time? They are both mine.
 mmkay. making sure. plagiarism is for dummies who don't have any original ideas.

and no, I was just trying to figure out how to fix my own roomba and came across both.
loadster4 years ago
That is an excellent dissection instruction. However, the key to a sustained restoration is to keep the rebuild within the confines of the original design.
I would suggest getting the replacement cells and triangle bit-tool from batteriesinaflash -dot-calm if you're handy with a soldering iron and flux and solder and return the old cells to radio slack where they ascribe to the Charge up to Recycle resource reclamation program and will route old cells to the right places.
We hope.
12V5 years ago
i checked a 7.2v rc battery and two cells were dead(one at the positive and one in the middle)
bill7355 years ago
Doing this with Room Discovery. 1st: Charged directly from charger for 3 days, power light went green, pushed Max, everything went red, no movement at all. 2d: Got into battery case with the Dremel, like cheese (thanks, sklarm). Everything looked OK. 3d: Volt test showed a strong 20 volts for a 14.4 3000 mAh pack! Stopped there before destroying anything. I need someone better with electricity than I am to tell me what gives here. Are the batteries overcharged, hence the 20 v.? Is the motor gone, hence no movement on pushing Max? Are the contacts bad? Gearing locked? Help, guys and gals. -Bill
bill735 bill7355 years ago
Well, first thing was to put it all back together and redo the supercharging/Max discharge sequence and observe a little more carefully, including listening to the Roomba's songs. In other words, start over. After reassembly and hookup, the charging light is showing green again. The requisite three days is Friday, so it'll be after that when I can reply again. -Bill
sklarm (author)  bill7355 years ago
Good question Bill. I'm not sure what the state of your batteries is at 20V. 3000mAh is a pretty high capacity cell, was that default with your irobot? It would be interesting to see what you end up doing here. Perhaps swap the cells with a new sub-c set just to see if you get a good runtime with your roomba. I plan on using a lithium-ion set in my next replacement. I have a lot of old laptop cells that can easily be repacked. The primary difference is I need to use a appropriate charger.
FKlusmann5 years ago
I opened a battery pack which would cause the iRobot to stop after 15 seconds. I measured 16.7 V across the entire pack (out most -red to inner -black and to the side - white connectors). Each individual cell gave 1.3 + volts. What is the component connected between the side terminal (white wire) and the negative (black wire) and could this be the cause om my failure? Thanks.
sklarm (author)  FKlusmann5 years ago
If all the cells are giving a voltage reading then it might just be time to swap them out for a new pack of sub-c cells. They have probably lost their ability to hold a charge. I believe the small component in the pack is a thermistor to measure any heat build up in the pack during charging.
Thank you for your fast response and fine instructable!
nickademuss5 years ago
Check eBay for several battery rebuild kits, Radio shack also had individual sub C sized cells available as well as most hobby shops that support RC cars. Also take note that the charging cycle for smaller cells is different from others and that different brands of cells will even charge and discharge at different rates. Thats why packs with all matched cells work best and longest. and run the fastest in RC car races. I match mine to within .001 volt. My little autonomous vacuum just got a rebuilt battery, runs fine now.... Nice post of the battery disassemble!
jaredharley5 years ago
Interesting - I have a Roomba that's got a battery life of about 10 minutes right now, and iRobot wants nearly $100 for a new battery pack. I plan on trying this out - thanks!
Thats a horrible idea. Not only is the battery a different size, its a completely different chemistry. Your AA has less capacity so it will discharge before the others. When you go to charge it is is almost gauranteed to overcharge and die. If your lucky it doesnt blow when it is dies.
sklarm (author)  Hands Without Shadows5 years ago
The difference between the battery I've used and the battery the iRobot products comes with is 11% in capacity. The roomba has a low voltage shut off that occurs at 50% capacity. I will never get near the full discharge. Your comment is not only incorrect, but also not constructive. There is a be nice policy on instructables. You risk being banned. Some other comments from "Hands Without Shadows": » Wait till your a little older. » You are not your father. Get him to read stuff like this over before someone kills them…
Sub-C and AA batteries have drastically different internal resistances. The internal resistance difference will make the AA discharge faster and kill it. Even if you never get near full discharge it doesnt matter. AA's are not designed for high current discharge like this, hence the difference in internal resistance. Btw, how did you attach that AA? I guess mature comments are incorrect these days. Why dont you go back and see what context those comments were made in? When I see bad ideas I call them out. Keeps people from wasting time/money or even worse, hurting themselves.
sklarm (author)  Hands Without Shadows5 years ago
I don't agree that sub-C and AA NiMH batteries that have very similar mAh and voltages would have significantly different internal resistances. However, you do have a valid point about internal resistance. As batteries age the internal resistance increases. If were to have ordered a brand new Sub-C 2600mAh / 1.2V / NiMH that matched the existing roomba pack it would have a different resistance than the other 11 roomba batteries because of the age difference. I believe that the internal resistance in this case is negligible. Whether it be a new Sub-C (not worth the money and shipping) or my 5 year old AA. I measured the voltage drop on each cell and my AA and found the values to all be within a .1V spread. There is no need to be fearful about hacking batteries. The only wrong thing to do is to throw away 11 batteries because thats what everyone else does. I zap my NiCd's with a welder to revive them. I have a desulfator I use on my lead acid batteries. Lets try and make them last. The NiMH 2300mAh AA was added to the pack using the existing tabs from the removed Sub-C battery. I used aluminum tape to hold the tabs onto the battery. Lets see how long this pack goes for. My guess is another 12 months. It would be nice to hear from iRobot on why this particular cell (2nd from the positive) is the most common to fail.
and it IS the same chemistry, lol NIMH
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