Usually for a robot vacuum the balancing and battery protection is in the pack. The robot vacuum may have an an additional temperature sensor or data lines to communicate with the battery. You'd have to open the pack further to where the 4 wires go and see what writing is on the PCB of the BMS.
What if my battery does not have a protective board?
If a lithium battery does not have a protective board, the three wires are: the red wire is the positive pole, the black wire is the negative pole, and the other color wires do not serve the function of providing the product motherboard to monitor the voltage of the lithium battery. Instead, these batteries should be handled with extra caution due to the risk of overcharging or deep discharging.
Most consumer devices that have lithium single-cell batteries have 4 connections. I've noticed the following diverse types of devices, this is true: The 4-connection rule seems to hold even with devices that have multi-cell batteries like cordless drills.
How many wires does a thermistor need?
This could occur if eg. the bike was run down-hill with a full charge. 2 wires connect to the battery, and in general the extra 2 wires connect to a thermistor to allow temperature sensing of the battery. Although for more efficient wiring this could be done with a common ground giving a total of 3 wires, which is rarely seen.
How do you know if a lithium battery is protected?
A 4s lithium battery has 0, 3.7, 7.4, 11.1, 14.8, and 5 different potentials. If it is a protected version, the two red and black wires should be internally shorted. The white wire is the flag of the protection chip. It is a high battery voltage when it is protected and a low voltage when it is not.
How do I know if my battery is a positive or negative?
If your lithium battery has a protective plate, the red wire is the positive terminal and the black wire is the negative terminal. The other colored wire is the NTC (thermistor) of the protection board.
The voltage range for a ternary polymer lithium battery should be between 2.8V to 4.2V. For comparison, the iron-lithium battery should be between 2.5V to 3.65V, and the lithium titanate battery between 1.6V to 2.8V.