If your Roomba sits on the base and the light never settles into a charge, start with the metal pads and the bin, not a new battery. The robot has to sit square on the dock, the contacts on both sides have to be clean, and the dock has to be plugged into a live outlet. A tilted bin, a film of dust, or a power strip that is switched off will look exactly like a dead battery.
Watch when the failure happens. A robot that beeps and backs off the dock is usually not lined up, or the contacts are not touching. A robot that sits quietly and never shows a charging light may have no power at the wall, or the contacts are coated. A robot that charges for a minute and then stops is a different problem, and the battery section below is the one to read. Those three patterns save a lot of guessing.
Other causes worth a look:
- The dust bin is missing, warped, or not pushed in until it clicks
- Hair or grit on the charging contacts of the robot or the dock
- The dock is plugged into a switched outlet, a loose power strip, or a dimmer
- The robot was started from a software update and needs a restart the manual describes
- The contacts are bent, blackened, or pitted
- The battery no longer holds a charge, which you only conclude after the checks above
Unplug the dock from the wall before you wipe the contacts. Do not open the battery pack, and do not pry the robot apart. If the pack is hot, swollen, or smells sharp, stop and follow the manufacturer's manual. WhichVac does not publish steps for cells or wiring.
Checking the contacts and the bin
Pull the robot off the dock and turn it over only as far as the manual allows so you can see the charging pads. On most Roombas they are two metal strips on the belly, matched by two pads on the dock. You want bare metal, not a gray film. Dust from drywall, cooking oil, and pet hair sticks to those pads and insulates them. A robot can look seated and still not make a circuit.
Then pull the dust bin. The bin is part of the body shape. If it is not fully seated, the robot sits high on one side and the pads barely touch. Look at the bin for a cracked latch, a filter that is so packed it will not close, or a corner that is bowed. Click the bin back in and press the corners. It should sit flush with the shell.
Use this short checklist before you blame the battery:
- Dock unplugged from the wall, not only switched off at a strip
- Both pairs of contacts wiped with a dry cloth
- No water left on the pads
- Bin clicked in and sitting flush
- Dock on a hard floor, not a thick rug that tips it
- Outlet tested with a lamp or a phone charger you already trust
- Robot placed so its contacts land on the dock contacts, not in front of them
The Roomba j7+ in the WhichVac catalog is a camera-navigated vacuum with a bagged Clean Base. iRobot does not publish a pascal figure or a runtime for it in the sources we used, so a short run time on its own is not proof the battery is failing. The Roomba Max 705 Combo is a vacuum-mop in the same catalog. WIRED confirmed an app map and a room itinerary and did not state suction, runtime, or the mop mechanism. Neither model should be opened to "see" the cells.
Getting a charge started again
Plug the dock straight into a wall outlet. Skip smart plugs and power strips for this test. A strip that drops power when a computer sleeps will strand the robot every night, and it will look like a charging fault in the morning.
With the dock unplugged, wipe the contacts on the dock and on the robot with a clean, dry cloth. If the manual for your exact model allows a melamine foam pad used dry, that is fine too. Do not spray cleaner onto the pads, and do not use a dripping cloth. Moisture on the contacts is its own failure. Let everything dry before you plug the dock back in.
Seat the bin, set the robot on the dock, and give it a full minute. You are looking for the charging indication your manual describes, not a guess from a different year's model. Light patterns change between Roomba generations. If the manual says a particular blink means "check the contacts," believe that page over a forum post about another robot.
If nothing changes, restart the robot the way the manual describes, then try the dock again. Keep the robot on the dock for a longer stretch only after you see a charging indication. A robot that never shows that indication is not "trickle charging." It is still not connected.
Run one more alignment check. Scoot the dock a few inches from the wall if the manual asks for clearance, and make sure the robot's bumper is not hitting a baseboard before the contacts meet. A dock shoved tight into a corner can make the robot look docked when the pads are a few millimeters apart.
Only use a dock and a battery the manufacturer lists for that model. A third-party base with the same shape can have pads in a slightly different place. If you are replacing a lost dock, match the model name in the manual, then compare the current listing. The j7+ ships with a Clean Base in the sources we cited. The Max 705 is a different robot. Do not assume one base charges the other.
Keeping the dock reliable
Once it charges, the job is to stop the film from coming back. Wipe the contacts every few bin empties, especially if you have pets or you run the robot through a kitchen. Grease aerosol settles on the pads and turns into a clear coat you can feel before you can see it.
Give the dock a permanent spot on hard flooring, with the clearance the manual asks for behind and beside it. Moving the dock "just for today" and plugging it into a different strip is how a working robot starts failing on Sundays. If you have to move it, put it back on the same outlet and square it up before the next run.
Leave the robot on the dock between cleans. A Roomba that lives under a sofa will start the next job half empty, and a weak start is easy to misread as a charger fault. The catalog does not treat a published day rating on a Clean Base as a battery rating. Those are different parts.
A few habits that prevent a repeat:
- Wipe contacts when you empty the bin
- Keep the dock off rugs and off switched outlets
- Click the bin in after every empty, even a quick one
- Read the light pattern in your model's manual instead of a generic chart
- Stop and unplug if the dock or the robot gets hot
When the battery or the robot should be replaced
Replace the approach, not just the part, when the simple checks fail twice. If the contacts are clean, the bin is flush, the outlet works, and the robot still will not show a charge, the battery or the dock is the likely leftover. Follow the manual for a battery the maker sells for that model. Do not install a random pack, and do not open a swollen one. Swelling, heat, or a sharp smell means you stop and use the maker's support path.
A battery that charges fully and then dies a few minutes into a normal job is a different article, but the door into that problem is the same: prove the robot actually charges before you shop. If it never reaches a full charge indication, a new side brush will not help.
It is also reasonable to retire a robot when the dock is discontinued, the contacts are burned, or the shell is cracked so the bin cannot sit flush. Burned contacts are a replace-the-dock problem, not a scrub-harder problem. Scrubbing blackened metal does not restore a pad that has arced.
If you are choosing a replacement from the WhichVac catalog, read the spec card rather than a slogan. The j7+ is a vacuum with camera navigation and a self-empty base rated about 60 days in the source we used. The Max 705 Combo is documented as a vacuum-mop with an app map, and several specs were not published in that write-up. Pick the one that matches whether you need a mop. Check the current price on the retailer page. We do not print an Amazon price here.