PRO12-48R Battery Discharge Indicator - US Seller Auto Ranging Battery Monitor - Connect to any fully charged lead or hot acid battery system and the meter will select the proper range, for 12, 24 or 48 Volt DC systems (not for 36 volt systems - buy PRO36FRC-R for 26 Volt systems)). Curve 1 - Standard Lead Acid batteries have a discharge curve of 10.4 volts empty to 12.34 volts full (multiply by 2, 3 or 4 to get the range for 24 or 48 volt systems). Curve 2 - For newer designed "hot" acid batteries with a discharge curve of 11.5 volts empty to 12.7 volts full as found on Exide and Trojan deep cycle batteries (multiply by 2, 3 or 4 to get the range for 24 or 48 volt systems). Normally closed relay output operation for controlling secondary devices, 5 volt logic- limited to 200 ma.Relay opens or closes (depending on how you wire it) when the display shows fully discharged - flashing red #1 and yellow #2 LEDs Works on lead and hot acid batteries as the meter can be set for one of two discharge curves found from different battery manufacturers. Exide, Trojan, Continental and Interstate batteries will NOT work on the standard meters found on the market today. The PRO12-48R resolves this issue as it can be wired to work on these newer type batteries or the standard lead acid battery.