Xiaomi M365 BMS
The Xiaomi M365 BMS (battery management system) is a small circuit board that controls various functions on the battery. All good lithium iron batteries have them. The BMS controls various features including: Over/under charging, temperature, output voltage, cell monitoring and effectively turns a battery into a smart battery.
The BMS has two Z fuses that kick in and break the circuit if to much power is pushed into the battery, effectively stopping the battery from catching fire. (remember the hoverboards that use to catch fire, this was due to defective BMS’s)
There is a reset button on the BMS as well as a 2 colour LED chip. When diagnosing Battery problems this LED is essential as it will tell you what the problem is.
Included in this kit is a BMS – with cables and thermometer fitted, 2 contact strips & 1 contact strip to BMS adaptor. You will need: Soldering iron, Stanley knife, Solder, Flux, solder removal pen, circuit board holder.
Xiaomi M365 BMS diagnostics
Your scooter is not powering on, the display or the motherboard may be the issue however first check the battery. If the battery is flashing Blue the battery is fine, it may simply be the on off switch that requires replacing the display, which can be found here.
The battery is flashing Red, if the battery is continuously flashing red, you will notice by testing with a voltmeter that the voltage is reading well below 36v however the 2 terminals on the side of the battery (that connect to the BMS) are reading a higher reading. This is a BMS failure.
There is no red LED however when you plug the charger into the wall a LED flashes red 3/4 times then turns off. If you then test the voltage on the 2 side terminals you will see a high voltage reading that does not drop (contact strips are loose and need soldering). If you test the side terminals and get a small reading or the voltage drops off down to 0v then unfortunately the battery has gone into deep discharge.
The only way to remedy this is testing every cell and the connections, which requires pulling the battery to bits. In this instance we would always point you towards a new battery as its just not economically viable to fix.
Replacing the Xiaomi M365 BMS
You have diagnosed the fault and its the xiaomi m365 BMS. When working on this battery please remember it is a live battery with an output of 40v plus. it is very easy to create sparks when using metal tools to short circuits.
- Remove the battery from the scooter. Carefully cut the plastic from around the BMS side of the battery and start cutting into the sealant to release the Circuit board. there is two clips at the top of the channel that its held in. Before removing the BMS unsolder one of the side terminal cables, this will make the battery safer to work on.
- Remove the BMS slowly and disconnect the plug that connects to the two contact strips. The thermometer is glued into the bottom of the battery so you may need to cut this out also.
- Using a clamp or helper clips you can start removing the old power cables from the old xiaomi m365 BMS and then transfer them to the exact same position on the new BMS. (steady hands required here, you must be careful not to damage the new board)
- re attach the contract strips plug and feed the thermometer into the battery case first. When you are happy it is in the correct place, re attach the side contact that you un attached at the begging of the job. The BMS should now start flashing blue, indicating that it is working correctly.
- Using a good sealant, secure the xiaomi m365 BMS making sure its in the channels on the case and not touching anything other than that. use some battery heat shrink to waterproof the battery.
- Test by attaching to the motherboard and turning the scooter on. if everything looks good, re attach the battery to the scooter. when re attaching the base of the scooter, use bathroom sealant to stop moisture getting into the scooter.
- A handy video if needed
Xiaomi M365 Bms shipping
The BMS is shipped in a letter box size box so will be delivered without issues and wont get left out in the rain
Shipping is free – Royal mail 48 (2-3 business days)
Faster shipping at checkout with royal mail 24 – 95% next day.