# Batteries fully charged after two days of fishing, but how?



## NealXB2003 (Jun 8, 2020)

On my tin rig, i've got 2 identical group 27 wet cells wired in series to run a maxxum 24v trolling motor. The big motor is cranked off the low side battery in that pair. I fished till past noon Saturday, on the trimming motor most of the day, and in current at times. Sunday we anchored up by a brush top and let a kid drowned crickets. Only bumped the trolling motor on low a few times thru these morning. When I got home, I decided to charge the batts with my portable charger instead of the on board charger (because it is only a 4 amp per bank noco). Keep in mind, this was hours after I was done fishing. To my surprise both batteries showed fully charged. I can see how the alternator could charge the one batt in the group that it's connected too, but the other should be down significantly. I got the volt meter out and that confirmed the one that is used as a cranking battery as well was at 13.0V and the other at12.9V. Those numbers sound high?


----------



## Smackdaddy53 (Dec 31, 2012)

No that is normal. 12.8-13.3v or so


----------



## NealXB2003 (Jun 8, 2020)

I guess I didn't ask that question clearly. How is the second battery in series (the one not connected to the cranking battery) fully charged after running the trolling motor for so long? It shouldn't be getting any charge from the alternator.


----------



## lemaymiami (Feb 9, 2007)

First off I wouldn't use batt #2 (the low side of your two batt setup) as more than an auxiliary starting battery... I'd want a dedicated cranking battery to go with those two batts for your trolling motor setup... Yeah I know extra weight (to go along with that peace of mind for me since I may go weeks without a day off in season...) when you find yourself running three batteries. My #2 (the low side) is connected by battery switch to my cranking battery so most of the time my cranking battery functions as a stand-alone but when needed I can switch to #2 for an emergency start (or actually double them up for some serious cranking power... ) 

Pretty sure what's happening is that your motor, when you're running it, is not only charging battery #2 but also overflowing up into battery #1... since batteries in parallel or in series will tend to level out if they're in good condition... My electrickery knowledge is barely adequate though (despite running and rigging boats since the early seventies...) so I'll be watching this thread for someone with more knowledge than I have... for a different explanation...


----------



## Mako 181 (May 1, 2020)

lemaymiami said:


> First off I wouldn't use batt #2 (the low side of your two batt setup) as more than an auxiliary starting battery... I'd want a dedicated cranking battery to go with those two batts for your trolling motor setup... Yeah I know extra weight (to go along with that peace of mind for me since I may go weeks without a day off in season...) when you find yourself running three batteries. My #2 (the low side) is connected by battery switch to my cranking battery so most of the time my cranking battery functions as a stand-alone but when needed I can switch to #2 for an emergency start (or actually double them up for some serious cranking power... )
> 
> Pretty sure what's happening is that your motor, when you're running it, is not only charging battery #2 but also overflowing up into battery #1... since batteries in parallel or in series will tend to level out if they're in good condition... My electrickery knowledge is barely adequate though (despite running and rigging boats since the early seventies...) so I'll be watching this thread for someone with more knowledge than I have... for a different explanation...


I carry a lot of weight.

I have a 24V trolling motor with two batteries that are dedicated only to the trolling motor. These two batteries are located in my bow hatch and are charged by a remote charger.

I also have 2 cranking batteries that start my motor as well as run the boats other items. Lights, radio, live well, and the like. These two batteries are on a off, 1, 2, and all switch. I run the boat in battery 1 position today and position 2 the next day.
I have never experienced any difficulties with this set up using it the way I do.


----------



## NealXB2003 (Jun 8, 2020)

I agree it sounds like some voltage from either battery #2 or the alternator is making its way to battery #1. That would be great if intended to function that way, but id think id see electrolysis if it found an unintended path. I wondered if current was somehow flowing between the two through the onboard charger. Noco gen2 mini - 2 bank/4amp per bank. 

Really hate to add more batteries. This is just a duck hunting boat really and lacks storage. And I only fish out of it occasionally to get into places that I can't reach in my 21'er. Electronics are minimal. I do carry a lithium jump starter in case I run the cranking battery down, but I've never needed it.


----------



## NealXB2003 (Jun 8, 2020)

Checked this morning after letting it sit overnight. One batt is at 12.86v, the other at 12.9.

I'm just baffled that no charging is required after that time on the water. Even though everything is performing as expected, I'm worried something is going to bite me in the azz in a future trip.


----------



## Onebadlarry (Oct 10, 2018)

How is your battery system configured? I’m trying to think of the setup in my head, but I suck at imagining. All I can picture is two group 27s in series running the whole boat..,


----------



## FlyBy (Jul 12, 2013)

Has to be through the onboard charger.


----------



## NealXB2003 (Jun 8, 2020)

FlyBy said:


> Has to be through the onboard charger.


That has been my suspicion too, just don't know how to prove it.


----------



## NealXB2003 (Jun 8, 2020)

This is the simplest diagram I could find online to explain my setup. The "positive 12v Battery One" lead cranks the motor. The 24v lead powers the trolling motor. 










Onebadlarry said:


> How is your battery system configured? I’m trying to think of the setup in my head, but I suck at imagining. All I can picture is two group 27s in series running the whole boat..,


----------



## Capnredfish (Feb 1, 2012)

Some way possible to back feed through on board charger when you connected the portable? Charge by motor could do same. Just a guess. Hook up charger and disconnect on board from second battery. Have voltage on those leads?


----------



## FlyBy (Jul 12, 2013)

I have basically the same set-up without an on-board charger. My "house battery" gets charged by the outboard but the other does not.


----------



## Vertigo (Jun 3, 2012)

The most obvious answer would be a short somewhere in the trolling motor that would allow voltage from the alternator to span both batteries. Run both batteries down, disconnect the trolling motor, go for a short run to let the alternator do its work, then check the batteries. If the house battery is charged and the other isn't, you've found the problem.


----------



## NealXB2003 (Jun 8, 2020)

FlyBy said:


> I have basically the same set-up without an on-board charger. My "house battery" gets charged by the outboard but the other does not.


That is the way mine historically worked. And the way I expected it to work.


----------



## LowHydrogen (Dec 31, 2015)

I would check the amperage. Volts are not Amps, a battery that's discharged a decent amount will still read the correct voltage unless it has something wrong with it, even though it's power is somewhat drawn down.


----------



## mro (Jan 24, 2018)

in your diagram where is the trolling motors negative lead attached?

As for power "back" feeding through the charger, shouldn't happen depending on how it's wired.
Battery chargers use a rectifier to change ac to dc.
When the charger is not "turned on" I don't see how it could affect the two batteries.
If it did have a short the charger should not work or might be in a rather dangerous condition.

Seems Capt. Lemays explanation with the info given is the closet to what's happening.


----------



## mro (Jan 24, 2018)

LowHydrogen said:


> I would check the amperage. Volts are not Amps,


Been awhile since I've been dealing with battery systems.
What Low says about volt/amps is true. It's called a "surface charge" and you need a "battery load tester" to accurately test a battery.


----------



## m32825 (Jun 29, 2018)

How about checking voltage on each battery with nothing running, then voltage on each battery with the outboard running? Seems like you should only see the starting battery voltage change, as now it is being charged. If the other one changes you've got a clue.


----------



## NealXB2003 (Jun 8, 2020)

I like that idea. Will do that asap.


----------



## Onebadlarry (Oct 10, 2018)

mro said:


> As for power "back" feeding through the charger, shouldn't happen depending on how it's wired.
> Battery chargers use a rectifier to change ac to dc.
> When the charger is not "turned on" I don't see how it could affect the two batteries.
> If it did have a short the charger should not work or might be in a rather dangerous condition.


I actually ended up speaking with two NOCO techs in regards to multiple bank on board chargers. They both told me they have safety features inside the system which would never allow for one battery to charge or drain into the other battery.


----------



## m32825 (Jun 29, 2018)

Onebadlarry said:


> I actually ended up speaking with two NOCO techs in regards to multiple bank on board chargers. They both told me they have safety features inside the system which would never allow for one battery to charge or drain into the other battery.


How something is designed to work and "how it is working now" can be different things. Since something odd is going on we should keep an open mind about possible causes. Good to know protections are designed into the product.


----------



## NealXB2003 (Jun 8, 2020)

Tested this weekend on the hose. No voltage flowing through either the onboard charger or the 24v TM circuit when the engine is running on the hose. Next step.... retest on the water.


----------

