The Trollbridge12X24® Combiner allows you to charge your 24 volt trolling motor battery from the 12 volt alternator on your main engine or trailer hook-up without any risk of discharging your starting battery. It works by automatically putting two 12 volt batteries in series when you need to run the trolling motor and in parallel for charging. Charging is automatic when the main engine is running and the starting battery has at least 13 volt charge. When not trolling, the second trolling battery backs up the first trolling battery which can be used as a house battery.
The Trollbridge12x24 is suitable for installations with alternators up to 100 amps and 24 volt trolling motors up to 85 amps.
For larger installations you can use the Trollbridge2400 for 200 amp alternators and motor up to 500 amps.
If you DO want to use your starting battery for running the trolling motor you should purchase the Trollbridge24
See report in Fish Alaska Magazine, Best Accessories for 2019.
Click image for large view.