Battery Configuration

Broncothor

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I am new so please forgive me if this is common knowledge. I just purchased a 2007 2275FSI. It has a battery in the rear which I know powers the motor. It also has a battery in each of the front compartments. One I know is for a trolling motor. I thought the other was a spare but it has wires attached. Is this a second battery for the boat? Is there a selector switch? Does this one power everything but the motor? I also found what looks like a shore power plug by the trolling motor battery. Before I start in hooking wires and testing I thought I would ask. Thanks
 

Vikingstaff

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I am new so please forgive me if this is common knowledge. I just purchased a 2007 2275FSI. It has a battery in the rear which I know powers the motor. It also has a battery in each of the front compartments. One I know is for a trolling motor. I thought the other was a spare but it has wires attached. Is this a second battery for the boat? Is there a selector switch? Does this one power everything but the motor? I also found what looks like a shore power plug by the trolling motor battery. Before I start in hooking wires and testing I thought I would ask. Thanks
Congratulations on your “new to you” boat. Fun! Fun!

TBH, the front batteries sound aftermarket previous owner installed type items to me. And as you said, at least one seems clearly trolling motor related, which makes sense with its placement. Any chance the second was was simply an additional backup for a trolling motor?

For motor and boat wired accessories, the typical dual battery with switch setup is going to have both batteries side by side, and a “perko” type switch somewhere nearby. They often will be in the back of the boat as well nearer the motor.

Thus, I lean towards both up front batteries being owner add-on accessory type batteries for say the trolling motor.

However, no real way to tell without tracing wires. Maybe they also used that second front battery to power an electric motor lift and mounted it on boat instead lift (very odd if so!), maybe it was to power other onboard accessories they added; such as a mini-frig or what not? Maybe something else?

Do you have pictures of batteries, their placemements in boat and to the degree possible, wiring of them that you can share in here?

There are a lot of smart technical DIY’ers in here that may be able to provide great insights to you with some visuals.
 

BulldogsCadillac

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Take a look at the trolling motor and see if there's a model number on it. It could also be that it is 24v model and the batteries are wired in series. If you have a voltmeter you could test the voltage, or also look and see if say there is a red positive coming off the positive on one battery (going to the motor) and a black negative coming off the same battery going to the positive of the other battery, and a black negative coming from that second battery to the motor.
 

Broncothor

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Ok here is what I have so far. The boat is in a slip as the trailer is under repair. So I can’t get under to look. The trolling battery seems self contained and has some converter that allow it to charge from shore power. The other battery up front has major cables attached that run somewhere but I can’t see where. I do not see a battery selector anywhere. My next step will be to listen to advice here and also maybe disconnect eAch battery one at a time to see what works? If the front battery is a “house” battery how would it stay charged?
 

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Broncothor

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Take a look at the trolling motor and see if there's a model number on it. It could also be that it is 24v model and the batteries are wired in series. If you have a voltmeter you could test the voltage, or also look and see if say there is a red positive coming off the positive on one battery (going to the motor) and a black negative coming off the same battery going to the positive of the other battery, and a black negative coming from that second battery to the motor.
I don’t have the trolling motor and I can’t follow the wires as the boat is currently in a slip.
 

BulldogsCadillac

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I don’t have the trolling motor and I can’t follow the wires as the boat is currently in a slip.
Ahh, gotcha, well then I guess take a voltmeter and put the negative lead on the negative of one battery and the positive lead to the positive of the other battery. If it reads 24v, then you know they are wired in series.
 

Broncothor

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The batteries are so far apart, I don't know that I can do that. I am hopeful the back battery is the cranking battery and the front battery is the house battery. If that is the case, can they both be charged by the motor and yet each have a designated function. I ask because I do not see a battery selector switch anywhere.
 

Joeb14

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If you want to determine if either of the front batteries is connected to the main power, ie starting circuit, then disconnect the rear battery, and see if the boat starts. If the motor doesn’t start, then the front batteries are independent from the motor. That might save you some time when tracing wires.
 

Broncothor

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Thanks, I plan to try that. My question is... if the motor does not have power when the back battery is disconnected, but the other electronics have power, then I appear to have a house battery. Is it possible for this house battery to be charged from the motor, but not connected to crank it? Or is the only way to charge a battery from the motor is to have it so it can also crank the motor. Forgive my ignorance there.
 

LaurencetheAdventurer

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Thanks, I plan to try that. My question is... if the motor does not have power when the back battery is disconnected, but the other electronics have power, then I appear to have a house battery. Is it possible for this house battery to be charged from the motor, but not connected to crank it? Or is the only way to charge a battery from the motor is to have it so it can also crank the motor. Forgive my ignorance there.
Absolutely - the batteries can be charged from a single source but power separate sources. NOTE, starting batteries require a lot of amp delivery = heavy wire - trying to do this over distance would require some unusually large wires.
 

Broncothor

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Thanks. The starting battery is right by the motor on the back. The other battery is way up in the front.
 

Vikingstaff

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You should try asking whomever you are buying it from if they mind provided the most recent contact information from whom they bought it from. They might give it to you, and that might let you contact he original owner easily to ask them directly.

This happened to me back in 2016. Was the Rep for my dad and step moms estates. Sold my dads Model A hot rod. About a year later someone contacted me with a question (that unfortunately I could not answer, but my dad would have been able to). The person I sold it to on behalf of the estate had flipped it, and new owner had some mechanical questions about it.

Anyway, you never know. Might be able to reach out to original owner that set it all up. No guess work then…
 

BulldogsCadillac

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The batteries are so far apart, I don't know that I can do that. I am hopeful the back battery is the cranking battery and the front battery is the house battery. If that is the case, can they both be charged by the motor and yet each have a designated function. I ask because I do not see a battery selector switch anywhere.
Just to be clear, I'm talking solely about the two front batteries. I assumed they were both just in the front corner seats. You could also try using just a piece of decent gauge wire to "extend" one of the leads.

As to the question about each having their own function, they "kind of" can, with the use of a switch, but if they are both able to be charged by the motor, then they would both be able to start the motor depending on the position of the switch. The only exception to this would be if you had one of the units (was it by Blue Seas?) That when it senses a charge coming from the motor it 'opens' and allows current to the battery to charge, but disconnects when there is no charge current present. Which is what I'm assuming @LaurencetheAdventurer is referring to.
 
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