Used Boat w/ Trolling and Starter Batteries Running in Parallel – Is this Safe?

Just purchased a used 1990 sylvan backtroller with 40hp Evinrude, bow mounted trolling motor and another trolling motor that can plug into the 3 pin plug near the transom. After the first time trolling motors went out on me I pulled them out to charge and realized the batteries are running in parallel. (- to – and + to +, this increases the AH but not the V). Searching forums I didn’t find much. First boat I have owned and so I am wondering:
1) is this current configuration safe?
2) is this safe for my batteries?
3) Community recommendations?

I’d really appreciate your responses!

Need to know if your t-motor is 12v or 24v ?

-J.

For a 12v trolling motor it is safe. It was a fairly common configuration when electric trolling motors first came out. The biggest issue is if you run down the batteries with the trolling motor they may not start the big motor. Another issue could be if the 40hp has enough stator or alternator output to charge the 2 batteries.

I have 4 batteries in boat.

2 in parallel run trolling motor.
2 in parallel run motor, graphs, accessories.

Hook your charger up to one battery.
That one charger will charger both connected batteries.

Yes safe.
You can link any number of batteries in parallel and keep the same voltage of one battery.

For wiring in series, each battery voltage adds together. 12+12=24, 12+12+12=36

Safe yes but I would make sure you have the same battery type for both. Not ideal if one is a deep cycle and other is starting. Deep cycles do not like to be charged every time the motor runs. They prefer a discharge and then charge. You can cause premature battery failure.

Okay thank you all for quick responses!

I couldn’t find any labels on anything but I’m assuming everything is 12v since the batteries were wired in parallel and everything was working fine the few times I was out.

@pat k , I guess I need to look up how to tell if my motor is actually charging anything since I’ve only had the boat a couple of weeks. That would be really nice if it did!

@supercat this is kind of what I feared. The battery trolling battery went bad first and was from 3/18, the starter seems fine and its from 2016.
I’ll probably try to separate the circuits after my fishing trip this weekend for longevity of the trolling motor.

I’m also concerned about my new deep cycle batt. I took it home two days ago, put it on the charger till it said full charge and then charged the starter batt. Just now put the charger back on and it say the new batt is only half charged. Could that be one of those things were a new batt needs to cycle a few times to get a proper reading or something?

At 2016 and 2018 you are on bowwored time. Usually 5 years is a good point to replace if not sooner.

I’ve had deep cycles last 8 years. Treat them right and they last. No reason to replace them until you need too.

Load test them if you can. You’ll know when it’s time to replace them.

Get a multimeter and check voltage before & after charging.