Amazon.com: Runleader 12/24V Battery State of Charge Meter Gauge, Lead Acid Battery Indicator, Battery Tester; Battery Discharge Alert, Use for Golf Cart,Fork Lifts,Star Car, Yamaha(BI001-12/24V) : Automotive
Amazon.com: PRO12/24FRC 12 or 24 Volt Battery Indicator Meter - Solar Panel or Marine Trolling Motor 12 or 24 Volts : Automotive
batteries - Charge at 24v and discharge at 12v for battery system - Electrical Engineering Stack Exchange