Documentation

Overview

The SHILLEHTEK 2x 18650 Battery Holder Box with 4 Wires is a dual-cell plastic holder designed for building 2S (7.4 V) lithium-ion packs with a balance tap. Two 18650 cells sit side-by-side, and the holder is pre-wired with four silicone leads: a main red (+) and black (-) for pack output, plus two balance leads that connect to the midpoint between the two cells. This is the standard wiring used to feed a 2S BMS or balance charger.

The holder is fully passive: no PCB, no protection circuit, no switch, and no cover. The cells are held by spring contacts at each end and a metal strap that ties the two cells in series internally. This makes it perfect for makers building 7.4 V e-bike accessories, motor-driven robots, RC builds, portable amplifiers, or any project needing more headroom than a single cell can provide.

Because the cells are wired in series, balancing during charge is essential to prevent one cell from drifting above 4.2 V while the other is still under-charged. SHILLEHTEK sells a matching 2S BMS with balance leads that drops directly onto these four wires.

At a Glance

Specifications

Wiring Guide

Code Examples

For a 2S pack reaching 8.4 V, use a divider that scales down to your ADC range. A 100 kΩ / 22 kΩ divider (gain ~5.5) keeps 8.4 V under 1.6 V at the ADC - well within both 3.3 V and 5 V boards.

const int VBAT_PIN = A0;
const float DIVIDER = 5.5;   // 100k / 22k
const float VREF    = 5.0;

void setup() { Serial.begin(115200); }

void loop() {
  int raw = analogRead(VBAT_PIN);
  float vAdc = raw * (VREF / 1023.0);
  float vBat = vAdc * DIVIDER;
  Serial.print("Pack: ");
  Serial.print(vBat, 2);
  Serial.println(" V (2S)");
  delay(1000);
}

#define VBAT_PIN 34
const float DIVIDER = 5.5;
const float VREF    = 3.3;

void setup() {
  Serial.begin(115200);
  analogReadResolution(12);
  analogSetAttenuation(ADC_11db);
}

void loop() {
  int raw = analogRead(VBAT_PIN);
  float vAdc = raw * (VREF / 4095.0);
  float vBat = vAdc * DIVIDER;
  Serial.printf("2S pack = %.2f V\n", vBat);
  delay(1000);
}

from machine import ADC, Pin
import time

vbat = ADC(Pin(26))
DIVIDER = 5.5
VREF    = 3.3

while True:
    raw  = vbat.read_u16()
    vadc = raw * VREF / 65535
    vpack = vadc * DIVIDER
    print("2S pack = {:.2f} V".format(vpack))
    time.sleep(1)

Frequently Asked Questions