Hart 20v Battery Pinout Diagram Fix Guide

Hart 20V Battery Pinout Diagram: A Complete Guide

Hart Tools has become a major player in the consumer power tool market, offering a versatile 20V lithium-ion battery system. Whether you are attempting to revive a dead battery, build a custom adapter to power other electronics, or simply troubleshoot a charger issue, understanding the Hart 20V battery pinout is essential.

Disclaimer: Modifying lithium-ion batteries can be dangerous. Batteries contain high energy densities and can catch fire or explode if short-circuited or punctured. The information below is for educational purposes. Always wear safety glasses and use insulated tools. Hart 20v Battery Pinout Diagram

3. Making a Universal USB Charger from a Hart Battery

Use B+ and B- to feed a 20V-to-5V USB buck converter (available on Amazon/eBay). The battery’s BMS will still protect against over-discharge if you run the USB port through the BMS output (not direct to cells). Hart 20V Battery Pinout Diagram: A Complete Guide

3. T1 & T2 (Temperature Sensors)

  • Wire color (internal): White / Yellow.
  • Function: These connect to one or two NTC thermistors (Negative Temperature Coefficient resistors) glued to the cell group. As the battery heats up during charging/discharging, resistance drops. The charger uses this to cut power above 50°C (122°F).
  • Reading them: Use a multimeter between T1 and B- (or T2 and B-). At room temp (25°C), you should see ~10kΩ. At 45°C, it drops to ~4.5kΩ.
  • Why two? High-capacity packs (6Ah or 8Ah) use two thermistors to monitor both ends of the series string.

Problem 2: Tool runs, but stops after 2 seconds

  • This is a BMS over-current lock. Measure voltage across B+ and B- under light load (like an LED bulb). If voltage collapses from 20V to 0V, one cell group has high resistance. Use the pinout to access individual balance leads and measure each cell group (should be 3.2V-4.2V each).

Internal Schematic (Simplified)

[B+ (T1)] ----[Cell 5+]
                 |
              [Cell Group]
                 |
[B- (T5)] ----[Cell 1-] ----+
                            |
[T3 (ID)] ------------------+ (resistor to B-)
                            |
[T2 (Thermistor)] -----[NTC]----+
                            |
                          [B-]

Pin 2: Thermistor (Temperature Sensor)

Lithium-Ion batteries are sensitive to heat. Inside the battery pack, a small thermistor (usually a 10k NTC resistor) is taped to the battery cells. Problem 2: Tool runs

  • Function: It changes resistance based on temperature.
  • Connection: It connects between Pin 2 and Ground (Pin 5).
  • Safety: If the battery gets too hot during charging or discharge, the thermistor signals the tool or charger to shut down to prevent thermal runaway.