Help me understand...

[cnollego]

So used boat that i've had for about 1.5 years.

Previous owner added a second battery and isolator kit. I added a NOCO 2 bank smart charger.

Boat started slowly a couple of times and dropped from 13vdc to 12.3vdc in fairly short order while listening to the radio with the engine off.

I've purchased a 27M and a 31M to replace these batteries. What I'm trying to figure out is the wiring...can anyone shed light on what cables are going where.

This is the only picture i have with me but these secondary wire leads go into the isolator and then into a Blue Seas battery switch. There are also two big inline glass fuses...like what you see on high end audio equipement.

I could figure it out but I'm bored at work...anything you see I should do differently. I did order two new battery boxes to tidy that up a bit but other than that...what would you do?

 

[Stee6043]

What I'd do differently:

Replace those batteries with two of the same size (both 31's)
Cover all of the terminals with boots
Praise the battery gods that you got 6 years outta that smaller battery

 

[cnollego]

I was going to go with the 27 as the starter...considerably more cranking amps than the 31 i bought...just not nearly the reserve. all I ever have on is the radios and GPS when the engine is not running. I get it, bigger is better.

 

[KevinC]

I was going to go with the 27 as the starter...considerably more cranking amps than the 31 i bought...just not nearly the reserve. all I ever have on is the radios and GPS when the engine is not running. I get it, bigger is better.

Go with two batteries that are the same. The 31s should be fine for starting - they easily start my 8.1s. If you want a little less maintenance go with the AGMs if possible.

-Kevin

 

[Hoplite808]

There are way too many wires going to those batteries first off.

From the photo you shared there isn’t enough information to determine how they are wired. What I can see is they share a single ground wire and are grounded in parallel with each other, which is fine although a split ring lock washer should be used with each nut securing the connection on the battery posts. Then the largest red wires should be the main feed wires to the battery selector switch but all the additional red wires some with no fuses are aftermarket add ons most likely. Those should have been wired to a buss block after the selector switch with breakers. I suspect the smallest wires that go to each battery and go to both terminals are the charger leads, also probably an aftermarket add on. Without knowing where all these wires terminate to it’s hard to say how it should be wired better.

 

[KevinC]

I was going to go with the 27 as the starter...considerably more cranking amps than the 31 i bought...just not nearly the reserve. all I ever have on is the radios and GPS when the engine is not running. I get it, bigger is better.

You could also split the banks to A/B/Both/Off with a switch but just make sure your charger could handle two banks.

-Kevin

 

[KevinC]

There are way too many wires going to those batteries first off.

From the photo you shared there isn’t enough information to determine how they are wired. What I can see is they share a single ground wire and are grounded in parallel with each other, which is fine although a split ring lock washer should be used with each nut securing the connection on the battery posts. Then the largest red wires should be the main feed wires to the battery selector switch but all the additional red wires some with no fuses are aftermarket add ons most likely. Those should have been wired to a buss block after the selector switch with breakers. I suspect the smallest wires that go to each battery and go to both terminals are the charger leads, also probably an aftermarket add on. Without knowing where all these wires terminate to it’s hard to say how it should be wired better.

+1 on this. You should definitely reduce the number of connections on your main batteries.

-Kevin

 

[km1125]

I was going to go with the 27 as the starter...considerably more cranking amps than the 31 i bought...just not nearly the reserve. all I ever have on is the radios and GPS when the engine is not running. I get it, bigger is better.

That sounds like a reasonable plan.

Personally, I don't like seeing 3 or 4 connections on every battery post. I'd be inclined to move the "secondary connections" (that I believe are going to a VSR) up to the battery switch if that's closer to the VSR (or "isolator"). Maybe even add a beefy negative buss bar for all the connections so there's only ONE connection on those posts of each battery.

And yes.. whatever you end up with have those positive posts covered up.

 

[cnollego]

10-4. Thanks you guys. Really wishing i would have taken more photos. I'll do so this weekend. I'll likely hook it up as is now and once i have more pics, we'll figure out how to make it better. The + will be covered however in the meantime.