Remove and Desolder the BMS Board
⚠️ Important Safety Notice
- Only attempt this if you are experienced with high-voltage lithium battery packs.
- Always wear protective gear (gloves, goggles).
- Work in a fire-safe, ventilated environment.
- Do not short any terminals or expose cells to heat or moisture.
- Do not use or keep any conductive tools (e.g., metal tweezers, screwdrivers) near the battery during the procedure.
- Keep your desk clean and free of unnecessary tools or objects.
- Ensure there are no liquids on or near the work area.
Required Tools & Materials
- Insulated screwdriver set
- T25 Torx bit (to remove the main battery)
- Soldering iron (with fine tip)
- Multimeter
- Heat-resistant gloves
- Safety glasses
- Kapton tape (optional)
- Plastic spudger (non-metallic prying tool)
Step-by-Step Instructions
1. Preparation
- Disconnect the battery from any bike system (here is how to do it).
- Place the battery on a non-conductive, fireproof surface.
2. Open the Battery Case
- Remove the battery from the bike using using a T25 Torx bit.
- (optional) Discharge the battery partially to around 30–40% for safety (34v).
- Use the multimeter to confirm voltage on main output terminals: VG (negative) and VP (positive).
- Carefully pry open the battery casing. Avoid using force near connector areas.
- Take a photo of the BMS wiring layout for reference.
3. Locate the BMS Board
- Find the BMS mounted near the end of the pack with balance wires, balance connector, temperature sensor, and main terminals: VG (negative) and VP (positive)
4. Disconnect Main Power Leads & Low-Voltage Wires
- This is the most dangerous step.
- Desolder the positive terminal first (VP / red).
- Carefully unplug balance connector, free up temperature sensors.
- Desolder the the negative terminal (VG, black).
- Use a high-power soldering iron to melt the thick solder from ends of the battery pack (not from BMS).
5. Remove the BMS Board
- Gently lift the board using a plastic/wood spudger.
- Avoid bending or stressing the board during removal.
Final Notes
- Double-check that no wires or terminals are left exposed.
- Store the removed BMS in an antistatic bag.
- Document the wiring for future installation or replacement.
Install the BMS Board
Battery Pack preparation:
- The battery pack’s total voltage must be between 34 and 37 volts.
- The battery pack uses a 10s4p configuration, consisting of 40 cells arranged into four parallel groups, with ten groups connected in series. Each series section should have a similar voltage. The voltage difference between the highest- and lowest-voltage sections must not exceed 0.25 volt. To verify this, measure the voltage of each section and compare the highest and lowest readings. If the voltage difference exceeds 0.25 volt, the cells must be rebalanced before proceeding.
- Find the Reset Pins of the BMS (RST and GND). For a recently received working BMS these pins should be shorted with a wire. This indicates the BMS is in a sleeping mode.
BMS installation
Reverse the steps outlined in “Remove and Desolder the BMS Board.” Please do not disregard the previous paragraph, as it is essential for a successful installation.
After installation, remove the short circuit between the RST and GND pins by desoldering the wire connecting them. Exercise extreme caution during this step, as the battery pack is fully connected to the BMS.