Here is a low cost led level meter for batteries. It's quite easy to configure and this is how it is done.
Step 1: The Battery Meter.
This useful meter is perfect to check the state of charge on any battery. To access it's internals, just pop off the back. Inside there are two potentiometers. One for hi value and the other for low value.
Step 2: A Bench Power Supply.
An adjustable voltage supply is necessary to properly setup the level meter.
Step 3: Setting the Hi Value.
The power supply needs to be set to the highest value expected of the battery. Using a precision screwdriver, the hi pot is adjusted until the blue led bar lights.
Step 4: Setting the Low Value.
The power supply set to the lowest acceptable battery voltage. The lo pot adjusted until only one red led bar is lit.
Simple, effective and low cost. Perfect battery meter!