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.
Step 1: 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
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
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
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
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.
Step 6: Bust Out Your Meter
Betcha your dead cell is the second one in from the positive lead. Lots of reports on this one cell dying first. I have found that the cells near the postive leads seem to always go first. I had to replace a battery in the golf cart today and you guessed it...the first one on the positive side had pretty much died.
Step 7: Bye Bye Dead Guy
Get the the dead cell out of the pack. This will take a little prying and some cutting of tabs. Try to leave yourself as much tab from the remaining batteries so you can easily get a replacement battery in there.
Step 8: Cheat the System
There is a lot of info on the web about replacing your dying roomba battery with 12 new cells. This is wasteful. Just drop in a standard AA NiMH. I had a 2300mAh one on hand. A 2600mAh would have been more appropriate to match the other cells, but I didn't want to give up my good new cells. This one is about five years old and still doing great. No need to buy new fancy batteries or replace them all. I bet you have lots of NiMH AA's cells handy. Putting the AA in at angle will ensure a good fit, notice I didn't get that part right.
Step 9: ReVolt
Our voltage has jumped from 15.87 to a ass kicking 17.10. Nice, this is how we do it. My usage of the orange tape was more about making a dynamite looking tight pack. This was actually a bad idea as the tape made it difficult to get the battery case closed. I ended up cutting most of the horizontal tape off.
Step 10: Pack It In
Now that you have your batteries giving you a good voltage just pack them back into the plastic case and get it back in your iRobot.
Step 11: Test Drive
I let my irobot charge for 30 minutes then watched it clean my floors for over a hour. Imagine what it can do on a full charge. I'm pretty thrilled that I revived my year old dirt dog with basically a AA battery and some tape. No need to order replacement cells or pay shipping and handeling. Next, I'm going to deal with a old iRobot scooba battery.