Deep Cycle Marine Battery Leaking - Overcharge or just time to replace?

[Worleybird89]

I've had my travel trailer since 2018. I've kept it in covered storage with no power hookup available. In August of this year, I moved it home to a new enclosed RV garage I had built. Since then, I've had the 30 amp shore power connected and the battery cutoff switched on. A couple weeks ago, I noticed what looks like battery acid below the battery boxes. I have dual deep cycle marine batteries connected in parallel. The batteries are in individual plastic battery boxes. There is no corrosion around the connection posts, but the two metal rails where the battery boxes sit have significant corrosion. When I unplug the shore power and push the battery test button on the panel, it shows full. I pulled the batteries out of the boxes and one of them had some liquid in the bottom and definitely had moisture on the top. I am assuming the moisture is coming from the caps on top of the battery. These batteries are 2 or 3 years old and were last fully charged in May of 2025. I typically camp at least a half a dozen long weekends per year, and previously, that's the only time they got charged. Is it just time for new batteries, or do I have some sort of overcharging situation? Pics attached of the ground below the batteries, the battery box rails, and inside both battery boxes.

 

[John From Detroit]

Sounds like overcharge or Shorted cell 7 years is in line with average battery life so that argues for failure of battery.


Two GC-2 in series should be treated as a single battery.
Some folks argue parallel batteries should as well.
But before we get too far. What converter on that roll-house?

 

[Mark_K5LXP]

Your observation one or both batteries are venting is likely accurate. Pop the caps and see what the electrolyte levels are. If one cell is markedly down from the others that can indicate a problem.

Your push to test level meter will not tell you a lot. For this discussion it's not telling us anything useful.

Ideally your converter would ramp back the charge rate when the batteries are full. Flooded batteries will vent acid vapor if overcharged, or if one or more cells are weak.

Wonder and guess, or measure and know. A timed capacity test (not a parts store load test) will reveal any battery issues. After that you can monitor the converter charge stages and see if that's on track. Ideally you prove the system out with what's there before you start throwing parts at it.

Can describe the test details if you choose to troubleshoot.

Mark B.
Albuquerque, NM

 

[richclover]

I see that your batteries are 2-3 years old. Check electrolytes level. Clean everything up. Battery terminal cleaner spray from NAPA or Walmart or where ever. Lotsa water. Battery terminal protection. Spray with WD-40 if nothing else. Turn off the battery switch. Sounds like your converter is overcharging. Buy a battery minder to keep your batteries topped up. Or just do a slow charge later when you’re ready to go camping again. When I was parked and plugged into shore power my battery switch was always off.

 

[Rene T]

Check every cell and make sure that none of the plates are dry. If you find one dry, just add enough to get the level just above the plates and no more. Then charge them. After they are charged, then is the time to fill them. Fill them to a point just below or just touching the vent tube.
If you fill the cells and then charge the batteries, the acid could boil over and come out from the top of the cells.

 

[TheBar]

Depending on where you bought your batteries one may have been on the shelf for years longer than the other battery. One battery may be failing and is forcing the other battery to be overcharged. Most auto parts shops can load test batteries. Also you can pop off the fill covers and shine a flashlight down each cell. If one cell looks white it is sulphated. Which means it is a dead cell and needs to be replaced. Sulfation is caused by infrequent or insufficient charging.

 

[Kirk]

If the batteries are original, then they probably are due for replacement. Do you check the electrolyte levels on a regular basis? If not, they most likely are low and that may be part of the problem. Over charging could also be a factor. It is likely time to consider new batteries, but I would also remove them and clean the battery area thoroughly with a mix of water and baking soda. You may even wat to repaint the area while you have them out. If you replace them and prefer not to do regular maintenance, then you would be smart to upgrade to AGM batteries.

 

[Worleybird89]

The batteries are not original. They were purchased in the spring of 2022. After being disconnected for several days now, they are reading 12.99 V and 13.01 V. Electrolyte level was even across all cells and just above the lead plates. The plates did not appear to be sulfated. The Manufacturer date stamp on both batteries is 1/22. I have one on a Noco Genius 5 smart charger and will recheck it tomorrow, then repeat on the 2nd battery. If they can't maintain over 13.2 V with no draw for more than a day or two, is that an indication they are spent? I think that could explain frequently kicking, or keeping the controller in Bulk/Charge mode for an extended period, and causing a boil over scenario? I am interested in the timed capacity test @Mark_K5LXP.

My Power Converter is WFCO model WF-8735P. It is a 3 stage converter:
Absorption Mode: 13.6 Vdc
Bulk Mode: 14.4 Vdc - Activates when system voltage drops below 13.2 Vdc.
Float Mode: 13.2 Vdc

If either one of my current batteries will hold a charge above 13.2 Vdc, I'll reconnect it, and test the controller thresholds in each stage.

Assuming the controller is functioning within specs, my current train of thought is to switch to AGM batteries. Google says this controller is not compatible with LiFePO₄ batteries, and I am probably going to get a different camper within the next 3-5 years, so upgrading to lithium does not make financial sense. Google says this controller does work with AGM batteries. If I go this route, should I still mount them on the rails underneath the camper, or can I move them up into the storage compartment? It might be easier just to cut out the battery rails and toss them instead of cleaning and repainting.

 

[Lou Schneider]

The batteries are not original. They were purchased in the spring of 2022. After being disconnected for several days now, they are reading 12.99 V and 13.01 V. Electrolyte level was even across all cells and just above the lead plates. The plates did not appear to be sulfated. The Manufacturer date stamp on both batteries is 1/22. I have one on a Noco Genius 5 smart charger and will recheck it tomorrow, then repeat on the 2nd battery. If they can't maintain over 13.2 V with no draw for more than a day or two, is that an indication they are spent? I think that could explain frequently kicking, or keeping the controller in Bulk/Charge mode for an extended period, and causing a boil over scenario? I am interested in the timed capacity test @Mark_K5LXP.

My Power Converter is WFCO model WF-8735P. It is a 3 stage converter:
Absorption Mode: 13.6 Vdc
Bulk Mode: 14.4 Vdc - Activates when system voltage drops below 13.2 Vdc.
Float Mode: 13.2 Vdc

If either one of my current batteries will hold a charge above 13.2 Vdc, I'll reconnect it, and test the controller thresholds in each stage.

Assuming the controller is functioning within specs, my current train of thought is to.h switch to AGM batteries. Google says this controller is not compatible with LiFePO₄ batteries, and I am probably going to get a different camper within the next 3-5 years, so upgrading to lithium does not make financial sense. Google says this controller does work with AGM batteries. If I go this route, should I still mount them on the rails underneath the camper, or can I move them up into the storage compartment? It might be easier just to cut out the battery rails and toss them instead of cleaning and repainting.

12 volt, 100 a/h LiFeP04 batteries are $200 each on Amazon. Less if you catch one on sale. Your converter will charge them to at least 80%, which doesn't harm the batteries. Higher if you activate the Bulk Mode 14.4 volt charging mode which will fill them close to 100%.

 

[Worleybird89]

12 volt, 100 a/h LiFeP04 batteries are $200 each on Amazon. Less if you catch one on sale. Your converter will charge them to at least 80%, which doesn't harm the batteries. Higher if you activate the Bulk Mode 14.4 volt charging mode which will fill them close to 100%.

I considered this, along with an external charger, but the ones I would want (after a couple of days of researching) would be reputable brand, bluetooth compatible, so I could see the charge levels, etc. Then I would also end up swapping out the controller, because it would be the right way to do it. I will definitely go all in with LiFePO4 on the next camper.

 

[TheBar]

If your batteries are reading 12.99+ after being disconnected for several days they are either in good shape or your voltmeter is faulty. I would suspect your charger is faulty.

 

[Gary RV_Wizard]

These batteries are 2 or 3 years old

Very near to 4 years old if dated 1/22. Probably have a year or maybe two left.

After being disconnected for several days now, they are reading 12.99 V and 13.01 V.

That's excellent. Still at 100% (above 12.7v) after several days (see the table in post #11)

If they can't maintain over 13.2 V with no draw for more than a day or two, is that an indication they are spent?

No, not at all. Lead acid battery voltage above 12.7 is residual "surface charge" from the previous charging cycle. Do not expect to retain 13+ volts once the charger if disconnected or turned off.

It's normal for an open cell lead acid battery to emit some acidic gases under heavy charging and those gases will condense on nearby surfaces. But you aren't seeing any signs of corrosion so that doesn't seem to be a problem worth worrying about. I'd be looking for some other reason there is liquid in the bottom of the battery box.

 

[bigbAZ]

If you're going to change campers in the near future I would just install a battery disconnect and leave them disconnected when not in use (after fully charging). The other option is a good charger like a Victron Blue Smart 4 stage configurable charger/maintainer.

While 12.7 indicates a fully charged FLA, when I had my FLA deep cycles mine would always read over 13 volts even after resting like yours are showing, and they would hold that for days. I tested with multiple testers including my Fluke 27. People tried to tell me something was wrong but there wasn't. I concluded that it's just the nature of different brands. Mine were NAPA brand 6 volt true deep cycle made by East Penn. I had a good run with those batteries even though the original owner had abused them in their first year by not understanding that you just can't let them completely discharge till your next trip.

 

[Mark_K5LXP]

Resting voltage for a flooded battery is 12.73V at 77F. Any higher than that is surface charge, or from an external connected source like a trickle charger or solar panel. For purposes of testing, lifting a battery cable is the only way to know the batteries aren't being charged or discharged. By definition the only accurate open circuit voltage test is after the battery has been sitting idle for 24 hours.

Open circuit voltage testing can show some indication of health but the real test is how much power they can deliver under load. The test that reveals merit is a timed discharge test. With this result one can know where the batteries stand, either to gauge replacement or suitability of purpose.

Before testing, know the batteries are fully charged. Not by assumption but by connecting a charger and leaving it to complete for 24 hours. If it has an equalization cycle even better. A battery can only deliver what's been put in it.

The test amounts to connecting a load that draws 1/20th the Ah rating of the battery. So for a 100Ah battery, you'd use a 5 amp load. These can be devices in the camper and done with the batteries where they're installed. Monitor the battery voltage with a meter, and note the time when the test started. How many hours the battery runs until the voltage goes down to 10.5V is the result. A good battery will go for 20 hours. 15 hours is 75%, 10 hours, 50%. Generally anything less than 50% is considered failed, some consider 80% to be the threshold to replace. The actual number one decides suitability depends on how they will be used short and long term. Cared-for batteries decline slowly, so even if they test less than 100%, if they meet your needs there's no urgency to replace. Do a capacity test as a part of routine maintenance and you will never be surprised by battery degradation.

Mark B.
Albuquerque, NM

 

[CharlesinGA]

The big question is if the converter is multi-stage and if it is dropping back to a maintenance voltage after a few hours.

A Progressive Dynamics converter (as an example) has a charge cycle like this.

The WFCO multi-stage converter is different but the same idea, dropping to a storage mode after a period of time. Problem is, you have a WFCO converter, and they are bad about not stepping down like they should. Someone had installed a WFCO multi-stage converter in my trailer to replace the original single stage unit, and I tested it several times, and it never dropped down to storage mode. I ditched it and installed a Progressive Dynamics 4645 converter.

I think that could explain frequently kicking, or keeping the controller in Bulk/Charge mode for an extended period, and causing a boil over scenario?

This is pretty much normal for WFCO junk. The batteries sound as if they are OK. Pitch the converter and replace it with something reliable ie. Progressive Dynamics.

Charles

 

[John From Detroit]

I ditched it and installed a Progressive Dynamics 4645 converter.

I like that for multiple reasons.. ONE When I got my class A in 2005 It had a PD 9180+wizard. I did some research and failed to find a better converter. Still have not... Second. PD helps pay for my retirement being as Michigan Company.

I've been to the factory (when my 9180 died) nice people.

 

[Worleybird89]

It's been a week with the batteries removed and disconnected. Both are holding at 12.96 Volts. Suspecting @CharlesinGA nailed it, and the converter is not stepping down to float mode. I pulled up the Power Dynamics website and the Converter Crossover Guide says I need a PD4135KV for lead acid or AGM batteries or a PD4135KW2BV if I want to go LiFePo4. I'm having a difficult time finding the PD4135KV in stock anywhere. The PD4135KW2BV seems to be available on amazon for just over $200 which is about the same price or cheaper than the out of stock PD4135KV price listings.

Questions:
- Should I consider LiFePo4 again? I am assuming the converter has to be replaced regardless.
- If the panel and cutout for my current converter with integrated panel, WFCO model WF-8735P, has plenty of space that I don't need the exact fit replacement, am I limited to just the two Power Dynamics models on the chart or will other more available models work? Current dimensions: 12'' W x 7-1/4'' H, 4-1/2'' D; Cut out: 10.44" W x 6.13" H. (See attached pic of current installation)
- Do I need to stick to a 35W converter or can I upgrade to a 45W or 60W model without rewiring stuff?
I need to stick with 30 Amp shore power. The replacement panel needs to support at least six 12V circuits and one 30 Aac Main circuit plus five 20 Aac branch circuits. It does not appear replacing just the converter alone is an option.

 

[Mark_K5LXP]

Should I consider LiFePo4 again?

Only you know your power usage, and if the benefits of Li is worth the cost and effort to implement. The converter is a consideration, but not the only one.

the converter is not stepping down to float mode.

Wonder and guess or measure and know.

Here's the multistage diagram from the WFCO user manual:

It would be a basic exercise to discharge the batteries some nominal amount, say 20%, turn on the converter and watch it step through the stages with a voltmeter. Before I'd go replacing something that might not be broken I'd run this simple exercise.

Mark B.
Albuquerque, NM

 

[CharlesinGA]

There is no need for you to replace the fuse panel, it is fairly new and if in good condition, don't mess with it. The wire hookups are the same.

Where did you get that converter number from, I'm not finding any PD4135 anywhere on the website.

Power-Converters - Progressive Dynamics

Here are the WFCO converter choices, I think you have the power center number and the converter numbers confused, there is no 8735 CONVERTER series listed., but there is a 8700 series POWER CENTER.

Converters – WFCO Technologies

WF-8700-AD SERIES – WFCO Technologies

My suggestion is to CALL Best Converter and tell them you have a WFCO 8735 power center and you need a new converter to go in it, preferably a PROGRESSIVE DYNAMICS unit. The last time I talked with them, they started to lead me astray but I realized what I needed and just ordered it. Generally, they do know their stuff.

If it comes down to replacing the entire power center, get a Progressive Dynamics panel, probably the 4000 series.

Charles

 

[Worleybird89]

Where did you get that converter number from, I'm not finding any PD4135 anywhere on the website.

Converter-Cross-Reference-Guide - Progressive Dynamics

The Mighty Mini Compact All-In-One System offers an AC/DC Power Distribution Panel and Inteli-Power Converter with Charge Wizard battery charging technology.

www.progressivedyn.com