Running mine currently on the TM batteries. Since the starting battery gets recharged while running, wondering if it would be better on the starting battery to dedicate 100% of TM batteries to TM.
I run 4 fish finders plus other things. This proved to be too much for the cranking battery.
I use two batteries in series for my 24volt TM. Since deep cycle batteries are designed to run loads over longer periods I wanted to use them to power my electronics.
You don't want to connect to just one battery as this creates an imbalance and will reduce the life of the battery. Also, there can be too much noise from the TM.
My solution was to use a 24 to 12 volt converter. It also isolates and conditions the power for a clean 12.3 volts. Even at the end of a long day of trolling I still have 12.3 volts to the fish finders.
I have a 4 amp total load but this is only 2 amps to each battery.
I'm not sure why this hasn't made it to bass boats. Blue water and RVs use this method to get 12v.