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Roomba Battery Replacement

The battery in our trusty Roomba Scheduler went kaput after about 2 years of use (not bad). It wouldn’t hold a charge; the Roomba would run for about 10 minutes and then quit. I looked on Amazon and found some battery replacement options; the usual APS batteries for $50-$80, or an interesting option: a Tenergy 3400mAH NiMH battery for about $28 with a handy little triangular screwdriver.

I decided to try the direct cell replacement; why not…any excuse to take something apart. The reviews on Amazon indicated that there was some work involved in opening up the old battery, but folks did a nice job of outlining the steps. I thought I’d do the same with some pics.

First, someone suggested attempting to take the old battery apart before ordering the new cells. Then if you break the old battery casing, you could simply order a completely new battery with casing so you’d have a working Roomba.

Back to ordering this set of cells and screwdriver. The new battery comes with the little triangle-blade screwdriver, but if you’ve never ordered one before, you need to find a way to get those screws out. My solution was to cut off the end of a large screw and use a Dremel to grind away the sides of the screw into a triangle shape:

I used a soft screw to make the grinding easier; I had to re-grind the screw several times because some of the battery screws were very tight.

Once the screws come off, you realize the top won’t just come off. It has been glued at the factory; this is the hard part. I used a razor knife to score the seam, then a small jeweler’s screwdriver and a mallet to break the seam all the way around. If you do this on a surface like wood, you can actually feel the seam breaking as you tap. Tap carefully; there’s a battery in there. Here’s a picture after I got it open:

Then you gently pull the old battery out; take note of the position of the wires:

Solder in the new battery. Always test the polarity of the leads before soldering in the new battery. Obviously you can’t just rely on the wire colors (though they did match up). I just tested red and black to be sure I had the polarity right. I’m not precisely certain what the white wire does; I gather it’s some sort of switching component for the thermal shutoff (prevents continued charging if the battery gets too hot). Before I soldered the joints, I put a bit of heat-shrink tubing on the wires. This is for safety; you don’t want the battery shorting out, and it’s a very tight fit in the compartment. Here’s my final soldering and heat shrink job (the blue tape is just temporary shielding for the red (hot) lead since I had it removed from the case to make soldering the other wires easier):

Carefully put everything back in the yellow plastic case, making sure the leads aren’t being pinched anywhere, and screw the top down. Here’s a closeup of the handy triangle blade that came with the kit.

The battery charged for about 3-4 hours in the dock, and Roomba runs wonderfully again! I ran it for about 90 minutes tonight; the light was still green (hadn’t even started to turn yellow) but the floor was so clean I didn’t see any reason to let Roomba run any longer.

Would I do all this again to save a few dollars? I’m not sure. Once you have the yellow battery casing apart (at least half the time for this project; it took me about an hour total), you can keep buying replacement battery cells and get them soldered together in maybe 20 minutes. So if your Roomba lasts for 3-4 battery changes you could save a reasonable amount of money.  But most Roombas probably wouldn’t last beyond one, maybe two battery replacements (our first battery lasted almost 2 years, longer than many Roombas I know of). Granted, until iRobot changes the battery system, this battery should work in almost any Roomba – and if you have to buy a new Roomba, then you have a spare. In any event, if you’re mechanically inclined and want to save a little money, this is definitely a workable solution for replacing your worn-out Roomba battery.