DROK 12V to 6V Battery Converter – Bat Conservation and Management, Inc.
How to charge two 6V Lead-acid batteries with 12V pulse charger (Two battery charge in series) - YouTube
Amazon.com: Lead Acid Battery Trickle Charger 6V/12V 10A Intelligent Auto Stop Charging Function with Bar LED Screen : Automotive
Amazon.com: Battery Charger Automatic 6V 12V 1.5A, Trickle Charger Suitable for AGM Gel SLA VRLA Flood Lead-Acid Batteries, Starting Batteries for Auto Car Motorcycle, Dual Voltage Output Detection and Repair : Automotive
NEXPOW Battery Charger - 6V/12V 1A Trickle Charger, Battery Maintainer for Car Motorcycle - Walmart.com