From bigclivedotcom.

Although intended for power tools, this module will also be useful for equipment with 5-cell lithium battery packs, commonly referred to as 18V batteries or sometimes 21V batteries.

The circuitry is very basic, with just four LEDs with resistors and zener diodes in series with them so they light at vague thresholds, and a small MOSFET with simple timer circuit to hold the display lit for a few seconds after the button is released.

For a specialist application you could swap the zener diodes for custom thresholds.

As supplied, the LEDs light up at the following thresholds:-

1 = 2.5V and above. It just has a resistor in series with the LED.
2 = 17.5V and above. That equates to an individual cell voltage of 3.5V. (10-20% charge)
3 = 18V and above. That equates to an individual cell voltage of 3.6V (30-40% charge)
4 = 19.3V and above. That equates to an individual cell voltage of 3.9V. (75% and above)

Because the voltage across the zener and LED will vary with current, there is a slight ramp of intensity with voltage at each threshold.

These modules are compatible with some generic Chinese power tool batteries, but in some cases the blanking plate where they go is actually moulded into the plastic.

If you enjoy these videos you can help support the channel with a dollar for coffee, cookies and random gadgets for disassembly at:- https://www.bigclive.com/coffee.htm
This also keeps the channel independent of YouTube’s algorithm quirks, allowing it to be a bit more dangerous and naughty.

#ElectronicsCreators