How to Remove the BMS Board from an SX3 Main Battery
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How to Safely Remove and Desolder the BMS Board from an SX3 Main Battery
⚠️ 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 Low-Voltage Wires
Carefully unplug balance connector, free up temperature sensors.
5. Disconnect Main Power Leads
This is the most dangerous step.
Desolder the negative terminal first (VG / black), then the positive (VP, red).
Use a high-power soldering iron to melt the thick solder from ends of the battery pack (not from BMS).
6. 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.
