Guide 7: How to measure the different cables of a robot vacuum dead battery?

ID: 218621

Description:

Taking advantage of the fact that I had a robot vacuum dead battery that came to me from a robot that was beyond repair, which has 5 wires, we are going to reverse-engineer it by disassembling it and seeing the purpose of each one of the wires.
These types of batteries are composed of 4 Li-ion, Lithium Ion 3.7V batteries, model 18650; the output amperage can vary from one model to another, this one is 2200 mA = 2.2 A.
Just remember that Lithium Ion batteries must be recharged with a voltage that increases progressively; they cannot be recharged like lead-acid ones at a fixed voltage.

Once the plastic casing is trimmed, we can see that the battery cells are connected in series, which was to be expected: 3.6 x 4 gives us the 14.4 V.
The two thick RED and BLACK battery terminals correspond to the 14.4 V.
The thin wires are soldered to the intermediate connections between each cell; this way, the device can compare the voltage of each of the 4 cells to determine if one is lower than the others. That is the "mystery of these wires."

Photo 1: Measurement of total voltage. It is always a value higher than the nominal voltage, in this case 15.60 V.
Photo 2: Measurement between the negative terminal and the yellow wire; we are actually measuring 3 dead batteries in series = 11.58 V.
Photo 3: Measurement between the negative terminal and the center tap of the 4 dead batteries; we are measuring 2 dead batteries, 7.7 V.

Photo of the hand-drawn schematic; when we don't have more information about something, we perform reverse engineering by disassembling it, measuring, and taking our own personal notes. A different technique helps each person, but this one has always been a great help to me.
Other guides on robotic vacuum cleaner batteries: Robot Vacuum Cleaner
End of the guide.

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