ネタ | machii-little道場 | コンピュータ | まにあ道

In the winter of 2021, my Eufy RoboVac 11S started acting up. It used to run for nearly an hour and a half, but suddenly, its runtime dropped to just over twenty minutes before it would scurry back to its charging dock—or sometimes, it would simply conk out in the middle of the floor, letting out a few plaintive beeps. At first, I assumed the dust bin was full or that hair had gotten tangled in the wheels, but cleaning it thoroughly didn't help. Later, I checked the official Eufy support page and learned that lithium-ion batteries typically have a lifespan of 300 to 500 charge cycles; if you run a full cleaning cycle every day, the battery’s performance can start to degrade noticeably after about a year. Doing the math, I realized I’d been using the vacuum almost daily for nearly two years—it was right at the end of its expected lifespan.

I was a bit nervous before opening it up.

Eufy’s official store sells replacement batteries for around $30, compatible with a whole range of models, including the 11, 11S, 11S MAX, 12, 15C, and 30C. I hesitated for a moment, wondering if I should just buy a new unit, but then I realized that, aside from the battery, my 11S was still in great shape—the suction was fine, and it navigated quite intelligently—so it would have been a shame to throw it away.

Once the replacement arrived, I flipped the vacuum over and found just two Phillips-head screws holding the bottom cover in place. Removing them revealed the battery compartment. The battery model was printed on the label: INR18650 MH1-4S1P, 14.4V, 3000mAh, 43.2Wh—consisting of four 18650 cells wired in series. To be honest, I had always assumed that robot vacuum batteries weren't user-replaceable. Seeing this setup, I was genuinely surprised—could it really be this simple? Just two screws?

I did get stuck for about five minutes, though. There was a plastic clip on the battery connector, and I was afraid to pull too hard for fear of snapping the wires. I ended up using a small, flat-head screwdriver to gently pry it open, and it popped right off—the whole process was far easier than I’d expected. A Japanese user mentioned in the reviews that the "connector was a bit stiff, but it was still easy to swap out," and that was exactly my experience.

It’s like having a brand-new machine.

Once the new battery was installed, the bottom cover snapped back on, and I placed it on the charging dock—the charging indicator lit up immediately. It took about four to five hours to reach a full charge. When I pressed the start button, the unit slid off the dock, moving with a noticeable snap and agility it hadn't shown before.

During its first full cleaning cycle, it managed to cover the entire area before returning to the dock on its own—taking about 72 minutes. It might not be "back to 100%" in the absolute sense, but it’s a massive improvement over its previous state, where it would run out of steam after just twenty minutes. I’ve read reviews stating that the MH1-4S1P battery cells maintain voltage exceptionally well under load, with each cell capable of handling a 5A discharge. I’m no expert on battery specifications, but the practical result is clear: with the new battery, this old machine can once again clean my entire 70-square-meter apartment from start to finish.

When it comes to batteries, things can be deceptively simple.

There’s a sea of ​​compatible batteries on the market, ranging in price from very cheap to moderately expensive. My advice: don’t just go for the cheapest option. The official Eufy battery is rated at 3000mAh, while some third-party alternatives claim 4000mAh or even higher—yet their actual capacity and discharge performance often fall far short. I saw one user comment that a third-party battery "died after just five months, whereas the original lasted four years"—a staggering difference. Another user from a Russian-speaking region complained that a replacement battery "lasted less than a year and had only a quarter of the lifespan of the original." Buying a cheap replacement twice often ends up costing more than just buying the official one in the first place.

As for how often you should replace it, Eufy officially states that their lithium batteries have a lifespan of 300 to 500 charge cycles, though the actual longevity depends heavily on how you use the device. If you run it twice a day, you might notice performance degradation within six months; if you only use it two or three times a week, it should easily last two to three years. After replacing the battery in my unit, I adjusted my usage strategy slightly: unless there’s a specific need, I don’t have it run every day—just every other day. It’s been going strong for over a year and a half now, with no noticeable drop in battery life.

A quick, perhaps unrelated, personal habit: whenever the robot vacuum returns to its dock to charge, I take a moment to wipe down the charging contacts on its underside with a wet wipe. I’m not sure if there’s any scientific basis for this, but it feels like keeping the contacts clean helps with charging efficiency.

What a battery taught me

I’m still using this Eufy RoboVac 11S today. The casing has a few dings, I’ve replaced the side brushes twice, and I’ve washed the filter countless times—yet the core components have never failed. Tucked away at the bottom, the INR18650 MH1-4S1P battery just does its job; I don’t even think about it when the vacuum heads out from its dock.

Sometimes I feel that many electronic devices don’t actually "break"—we just give up on them. We replace a computer because it starts lagging, a phone because the battery degrades, or a robot vacuum because its runtime gets shorter. But if you’re willing to spend twenty or thirty yuan and ten minutes turning a couple of screws, many of these things could keep serving us for a long time. That’s what this 11S has taught me: it’s nothing fancy—it’s simply repairable, easy to fix, and keeps on working once repaired. For a household appliance, that’s arguably its greatest virtue.

Vacuum Cleaner Battery MH1-4S1P For RoboVac Eufy INR18650 MH1-4S1P