Roomba 530 doesn’t hold a charge

I bought a refurbished Roomba 530 on Woot in 2009, and it’s been an indispensable part of the household ever since. Sure, the cat hates it, it regularly knocks things over, and it somehow escapes its constraints and sneaks off into other parts of the house, but the point is, it cleans while I do something else.

It’s always a satisfying moment when I start the dishwasher, the washing machine, and Roomba at the same time and shout, “Get to work, robots!” and then leave.

One fateful day in 2018, I spilled some water* and Roomba, hapless as ever, bee-lined straight into it. It stopped. Its light turned red. It sang out some tones in a minor key that fit the rhythm of, “Uh-oh. What have I done?”

I let it dry out. I recharged it. Roomba still worked, but after only a minute it would sing the same sad song and claim that it was out of power.

I googled this problem and found a site where someone said, “Oh yeah, won’t hold a charge after getting wet? That’s definitely a motherboard replacement.”

I called iRobot support first, and asked if they could recommend an authorized repair shop in my vicinity. Oh no, they said, the motherboard is not a user-serviceable part. Perhaps you would like to check out our deals on the 900 series Roomba?

iRobot doesn’t sell replacement motherboards, so I turned to eBay. I don’t know where they come from on eBay — they must be salvaged from other Roombas, but how? Who does this? I bought a replacement 500 series motherboard, technically a model 540 motherboard, for $50.

Following RobotShop.com’s Roomba 500-series motherboard replacement tutorial, I successfully disassembled and re-assembled my Roomba. I was only missing one screw when I put it back together. I let Roomba charge fully, and they I tested out my newly-repaired robot.

Same problem.

Well, at least it turned on. I hadn’t made the problem worse!

I went back to Google and leaving the spilled liquid out of my queries, all signs were now pointing to a bad battery. There were two suggestions:

• Follow a simple battery reset procedure and let the Roomba recharge, or
• Replace the batter pack

Naturally I tried the reset option first, but it didn’t appear to help. I ordered a replacement battery pack for $25. Replacing the battery pack is much, much simpler than replacing the motherboard and requires very little disassembly. I put in the new battery, let it charge fully, and then gave Roomba another try.

The result? Roomba is now unstoppable. And possibly slightly smarter, thanks to the motherboard upgrade from 530 to 540.

My robot repair misadventures were due to a few mistakes I made:

• I assumed that the problem was due to encountering liquid, since the problem happened immediately afterwards. A classic logical blunder: Post hoc, ergo propter hoc. After the fact, therefore because of the fact.
• I relied too heavily on the first Google result I found that appeared to address my problem.
• I ignored the obvious: if the battery won’t hold a charge, maybe the culprit is the battery!

If you have a Roomba that seems to tire quickly, consider trying the battery reset, but a replacement battery pack may do wonders. Roomba uses Nickel metal hydride (NiMH) batteries, so make sure you recycle/dispose of the old battery pack responsibly.

* By water, I mean part of a vesper martini I had just mixed. “Oh dear I’m afraid Roomba’s found the gin,” may be one of the most ridiculous sentences I’ve ever uttered.