A Neato robot vacuum in their initial XV series product line is powered by a pair of identical 6-cell NiMH battery packs. When I picked up my XV-21 from a local thrift store it did not power up, a fault which I’ve isolated to its failed battery packs which I’ve since replaced to get the whole system back up and running with help of [Emily]’s loan of Neato charging dock. When I evaluated my battery replacement options earlier, one was to buy new cells and rebuild the pair of packs myself. I rejected that option because new cells actually would have cost more than pre-built replacement packs.
But since then Emily found a second thrift store Neato, a XV-12 with its own failing battery pack. This makes a total of four identical 6-cell NiMH battery packs. What are the chances we have sufficient good-enough NiMH cells in this pile for one set of healthy batteries? It costs nothing but a bit of time, well within the spirit of the kind of projects we tackle at SGVHAK meetups, and so it’s worth a shot.
First, the XV-12 battery packs were trickle charged overnight to get a sense of their capabilities, just like I did for XV-21 batteries earlier. Fortunately, the self-discharge profile looked promising.
Pack A: 7.93V self discharged to 7.64V after a few days.
Pack B: 6.59V self discharged to 5.98V after a few days.
Judging on voltage level alone, pack A is in better shape than pack B. The latter shows signs of having one completely dead cell. They’re certainly in far better shape than XV-21 battery pack. Out of 12 cells, only 1 held itself at ~1.3V after a week. The rest all self-discharged to a level ranging from 0.9V to flat zero after a few days.
So we disassembled pack B and deployed a volt meter to verify there is one cell that could only deliver around 0.1V. This cell was marked with an X and removed from the pack. Since we don’t have a battery spot welder available, we took care to make sure we keep the tabs on this pack.
The only not-dead cell from the XV-21 pack was marked with a check and removed from its pack. And again we took care to keep the battery tabs, this time making sure it stays with the ‘good’ cell.
With the battery tabs intact, it was easy to solder a new pack together.
A dab of hot glue helps the cobbled-together pack stay intact for installation into vacuum
When we turned on the robot vacuum, it no longer displayed a battery issue error screen, which is a great sign. We then left the robot sitting on its charger for about half an hour, then pressed the big red button to start a vacuum cycle. The vacuum suction motor turned on (Yay!) the brush motor turned on (Yay!) the robot started to move (Yay!) and then it went dark. (Noooo!) When we tried turning it back on, the error screen returned.
Our little cell-swapping experiment did not result in a battery pack capable of running a Neato. It might find a future life powering low drain electronics projects, but it wasn’t enough to run a robot vacuum’s high drain motors. Emily ended up buying new battery packs as well to restore her XV-12 back to running condition.