Bellow it is the quick presentation of 12V MF Battery Charge Tester, that is on-board over the battery.
Specific PCB was over a YUSUBA YTX4L (iGEL) 12V 4Ah /10HR.
Three LED indicators:
RED / Low = 12.1V or Less --- test current 12mA
Yellow / Charge = 12.5V --- test current 16mA
Green / Good = 12.8V or more --- test current 16~21mA
29 uA (constant PCB consumption)
Hart of the circuit IC, this is LM358
R10 missing or never installed.
My upcoming project, this is finding a way so to reuse it.
Photographs bellow.