Housekeeping battery issues: 1 overcharged.

K

KJ Hinton

New Member
Jul 6, 2021
10
Boat Info
1988 Sundancer 268 Alpha 1

2000 Ford F350 Diesel Dually 4X4
Engines
7.4 Gasoline Mercury
Newbie owner with a boat that needs work but was very cheap. It's an ongoing project that I'm clearly over my head with.

One of the things we needed to do was to replace the batteries, which I did using NAPA deep cycle Marine 6 volts (X2) about a month ago. One of the replaced batteries appeared to have boiled at some point; the case was obviously pushed out, though not cracked.

I wired them in series per the charts I've seen, and until today, there wasn't any problem. Outside temperature is about 85.

But while I was doing some work with the engine access hatch open, I noticed one of the 2 6 volts had fluid on the top... and there was some soft buzzing noise going on. (For safety reasons, I've kept the engine hatch fully open or off altogether during this time to avoid any build up of any fumes) This hot battery came from the same position as the battery replaced which appeared to have boiled.

I immediately killed the master switch on the panel and disconnected the 110 current.

Of the two batteries, the one with the fluid on top (electrolyte, no doubt) was very warm; not what you would call hot. The other 6 volt is completely cool to the touch, no fluid showing.

The hot 6 volt showed 6.97 volts when I checked it, the cool one is at 6.20.

All systems seem to be working OK. As I said, both batteries have been in there for a month, and the battery tender/charger is a ProCharger 120 which, allegedly, is supposed to avoid overcharging batteries.

https://www.tarampstore.com/power-supply-battery-charger-taramps-procharger-120a/p

The connections all are tight. And... I'm out of ideas.
 
Are you sure that the batteries are wired in series, and not in parallel? That is that positive on one of the to the negative on the next one. And the charger connected only to the outside posts (meaning NOTHING ever connected to the posts used for the one cable linking the 6v positive to the other negative.)
 
reading through the link you provided - i would guess that this is not an adequate marine battery charger. It seems to be more of a power supply than a charger - and makes many references for car audio. my guess is that its cooking your batteries because it doesnt know how to charge and float properly. suggest you look into a promariner charger.

https://www.promariner.com/en

if you are in a jam financially, you could turn the charger on for short periods to top off the batteries - juat dont leave it on for more than x-hours (prob 4-6hrs) at a time. also check fluid levels and add distilled water as needed to prevent the batteries from boiling dry.
 
If you're running two six-volt batteries in series, how is your charger connected to them? I ask only because, if you're running a 12 volt charger, it should be wired such that the charger "straddles" both batteries so that you're not applying 12 volts to single a 6 volt battery. If it happens to be across just one of the two, that would make sense as to why it's getting overcharged. As for the old battery you pulled out with the swelled case, that usually comes about by a fully discharged battery being frozen.
 
I am curious why you would use two 6v in series when a nice group 27 or 31 is what you needed?

That said, two 6v batteries in series are not going to act like a single 12v battery to that battery charger.
 
SKybolt said:
I am curious why you would use two 6v in series when a nice group 27 or 31 is what you needed?

That said, two 6v batteries in series are not going to act like a single 12v battery to that battery charger.
Click to expand...
That's an R/V "trick", as they suffer the same malady. The problem you can run into with two 12V batteries in parallel is there's usually no way to isolate the two batteries from each other (think "ground loop"). Batteries aren't perfect, and there'll always be one battery that has a slightly lower resting voltage than the other. While you're actively using your boat (summertime), there's typically no issue. However, if the boat sits unattended for any length of time, the two batteries are still connected together, even if you have your master switch off. In this case, there'll be a small but steady flow of current, and dead battery(ies) ensues. So, using two six volt batteries in series removes that loop, thus stopping all current flow.
 
Nater Potater said:
That's an R/V "trick", as they suffer the same malady. The problem you can run into with two 12V batteries in parallel is there's usually no way to isolate the two batteries from each other (think "ground loop"). Batteries aren't perfect, and there'll always be one battery that has a slightly lower resting voltage than the other. While you're actively using your boat (summertime), there's typically no issue. However, if the boat sits unattended for any length of time, the two batteries are still connected together, even if you have your master switch off. In this case, there'll be a small but steady flow of current, and dead battery(ies) ensues. So, using two six volt batteries in series removes that loop, thus stopping all current flow.
Click to expand...

so your saying that two 6v batteries in series wont self discharge like two 12v in parallel? kinda makes sense - given the two 12v batteries are trying to charge/equalize each other.. mainly applies to long term storage correct?
 
Nater Potater said:
That's an R/V "trick", as they suffer the same malady. The problem you can run into with two 12V batteries in parallel is there's usually no way to isolate the two batteries from each other (think "ground loop"). Batteries aren't perfect, and there'll always be one battery that has a slightly lower resting voltage than the other. While you're actively using your boat (summertime), there's typically no issue. However, if the boat sits unattended for any length of time, the two batteries are still connected together, even if you have your master switch off. In this case, there'll be a small but steady flow of current, and dead battery(ies) ensues. So, using two six volt batteries in series removes that loop, thus stopping all current flow.
Click to expand...

I get what your saying and totally agree on the one battery always charges the other and will eventually go dead faster as a result. But I still say a single group 27 or 31 is the better way to go. If more current is needed then a 4D will work and take the same amount of room and last longer. Unless your talking house batteries or diesel engines, then an 8D is the way to go. Just my opinion or I should say experience.
 
Series of 6v golf cart batteries are commonly used in boats (like mine for the past 12 years) and in RVs and, guess what, electric golf carts!

All batteries are separate single battery cells connected in series. A 12v has 6 cells normally and a 6v has 3. The fact that the two 3-cell batteries are wired to the next externally from the battery case doesn’t change how they work.

The advantage of a 6v series compared to a 4D or 8D is they are individually lighter so easier to move around and install. And you can configure the capacity you need with two matched high capacity 6v.
 
Creekwood said:
... The advantage of a 6v series compared to a 4D or 8D is they are individually lighter so easier to move around and install. ...
Click to expand...

Can't argue that at all, my 8D's are back breaking to swap out.

I like @Nater Potater ground loop explanation the best, makes sense for gas engines or 24v diesels.
 
Is that ProCharger 120 mounted in the engine room? If it is, it needs to be rated ignition protected. Automotive chargers are generally not rated as such.
 
Batteries in series will not equalize and one can overcharge while one undercharge regardless what mode the 12V charger is in. Batteries in parallel will equalize and all will balance to their natural resting voltage together.
You will need a battery equalizer/balancer to fix the issue when in series.
 
Last edited:
Over the winter, I think each battery should be isolated with its own float charger even if in parallel while in operation. Or just leave them in parallel with no charger as stated by poster.
 
Arminius said:
Over the winter, I think each battery should be isolated with its own float charger even if in parallel while in operation. Or just leave them in parallel with no charger as stated by poster.
Click to expand...
Except not when they are 6v batteries unless you have a 6v charger, which was the OP's original issue.
 
Is that charger marine rated? does it have a three wire AC connection or two? Many automobile chargers combine the neutral and ground wires into one connection. This is dangerous on a boat as it can send high voltage through your bonding system.

It appears to have a constant voltage setting instead of using multiphase charging that ends up with a lower voltage float setting. A constant high voltage charge is a sure way to boil your battery dry.

For charging batteries in series, the positive connection should be on one of the two batteries and the negative connection should be on the other battery.
 
Creekwood said:
Are you sure that the batteries are wired in series, and not in parallel? That is that positive on one of the to the negative on the next one. And the charger connected only to the outside posts (meaning NOTHING ever connected to the posts used for the one cable linking the 6v positive to the other negative.)
Click to expand...


Well, here's the diagram I used.

iu


Does that mean you believe 12 volts have been running to the first battery and nothing to the second? When I installed the batteries, the second one indicated 6.20 volts, the first (the hot one) indicated 6.30. I didn't notice the difference as being out of the ordinary.
 
markrsimon said:
reading through the link you provided - i would guess that this is not an adequate marine battery charger. It seems to be more of a power supply than a charger - and makes many references for car audio. my guess is that its cooking your batteries because it doesnt know how to charge and float properly. suggest you look into a promariner charger.

https://www.promariner.com/en

if you are in a jam financially, you could turn the charger on for short periods to top off the batteries - juat dont leave it on for more than x-hours (prob 4-6hrs) at a time. also check fluid levels and add distilled water as needed to prevent the batteries from boiling dry.
Click to expand...

Well, it's actually the charger that came with the boat. The batteries have been hooked up to it for at least a month.
 
Nater Potater said:
If you're running two six-volt batteries in series, how is your charger connected to them? I ask only because, if you're running a 12 volt charger, it should be wired such that the charger "straddles" both batteries so that you're not applying 12 volts to single a 6 volt battery. If it happens to be across just one of the two, that would make sense as to why it's getting overcharged. As for the old battery you pulled out with the swelled case, that usually comes about by a fully discharged battery being frozen.
Click to expand...


OK. Check to make sure it's straddled, one to the positive on one battery, to the negative on the other so the charger sees one 12 volt battery, so to speak.
 
SKybolt said:
I am curious why you would use two 6v in series when a nice group 27 or 31 is what you needed?

That said, two 6v batteries in series are not going to act like a single 12v battery to that battery charger.
Click to expand...


Rookie mistake? I went with 2X6 volts because that's what was in there when I got the boat. I've since read a few debates (2X6V or a single 12V deep cycle?) but the die was cast, so to speak.
 
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