New 6v house batteries & main battery losing charge

Let me ask you a question. Once your batteries have been on the charger overnight and then you remove the charger.....exactly what are you expecting the voltage to be on the batteries?

Charging voltage is different from the battery voltage. You can't expect the batteries (once charged) to stay at the charging voltage rate. They will automatically drop down to their "full charge state" which is 12.6 to 12.8 volts.

I think you are making much to do about nothing.

Ron

From what you describe there is nothing wrong with your batteries ..while Under use voltage does drop. If your reading it while using it
I think the Trojan batteries were fine :-( they should last years esp if you test them and they can hold 12.6. + volts

^^^^ The generator powering the ac charger is usually fastest.

New question which will charge coach batteries quicker/better absent an ac charger the generator 7 kw or the alternator?

Hi, Bill here, Pink Leopard's other half. I've been working on the batteries while she posted here. I noticed for the first time while we were in Mexico boondocking this winter that the battery voltage dropped rapidly from 13.4 to about 12.7 after charging with the generator. This did not jive with my previous experience, but in hindsight, that may have been more of an observational disconnect than an actual change in performance. This led me to believe that my 2-year old batteries had lost their ability to hold a charge. We bought the batteries in Yuma, so planned to stop there after leaving Mexico and replace the batteries and get a prorated discount because they had a 5-year warranty. When I called the store where I bought them, I was told that Trojan wouldn't honor the warranty because I hadn't followed their maintenance guidelines, which were onerous to say the least--required charging to 14.8 volts twice a day, weekly testing with a hydrometer, monthly or weekly desulfating, etc. etc. etc. I was told that I could come in and for about 5 or 600 dollars they could install all the appropriate systems to maintain my batteries. Given the cost of new batteries and the amount of time I expect to keep the RV, I replaced the batteries at Costco, and low and behold the new batteries did the same thing.

Then yesterday, while lowering the leveling jacks, I noticed the battery indicator light blinking on the dash. I checked the voltmeter and saw that both the house batteries and the chassis battery were rapidly dropping, the chassis battery was dropping even below 12.7. I checked the water level in the chassis battery, which was a bit low, added about two hydrometer bulbs full to each cell, charged overnight, and checked the voltage this morning after turning off shore power. Similar result, both house and chassis batteries dropping to 12.8 but holding there. Having just had work done at the Ford dealer to fix and overheating problem, I feared they may have had something to do with what I perceived to be a battery issue, but was puzzled as to what that might be. After reading these posts (thank you all), my concerns are shifting.

It seems the voltage drop is normal. I'm wondering if the service work somehow affected the alternator's ability to charge the battery. That would explain why the light came on after having just driven 5 hours. The battery should have been fully charged--the water was down but the cells were fully covered. We don't have too much more driving to do before workcamping for the summer, but I'll be checking the batteries after driving to see if the alternator is keeping them charged. I'll also be contacting the service center today.

Thanks again for all your input.

Bill

PinkLeopard wrote:
Aren't you supposed to be able to charge them up to 14+ and when it shows around 12.5 you're supposed to charge them.

Recharge closer to showing 12.0 to 12.2 zone under light load. 12.0 to 12.2 under light load is about 50% charged.
Yes you will be charging at 13.6 to 14.8 volts is normal. Once fully charged the new batteries will rest at about 12.7-12.8 volts with no load or charging.

Lots of good reading here:

The 12 volt Side of Life

Consider this handy STATE OF CHARGE chart...


Also consider this report from Progressive Dynamics on how long it takes to charge a deep cycle battery.

"Progressive Dynamics ran this test on the amount of time it took a PD9155 (55-amp) converter/charger set to three different output voltages to recharge a 125 AH (Amp Hour) battery after it was fully discharged to 10.5-volts.

14.4-VOLTS (Boost Mode) – Returned the battery to 90% of full charge in approximately 3-hours. The battery reached full charge in approximately 11 hours.

13.6-VOLTS (Normal Mode) – Required 40-hours to return the battery to 90% of full charge and 78-hours to reach full charge.

13.2-VOLTS (Storage Mode) – Required 60-hours to return the battery to 90% of full charge and 100-hours to reach full charge."

This is battery charging science - not many ways to get around it...

When camping off the power grid you want to watch your battery voltage and when it gets down to around 12.0VDC (approximately 50% SOC) then you want to do a smart mode charge starting out with 14.4VDC for two hours and dropping back to 13.6VDC for another hour (three hours total) to get your battery back up to its 90% SOC. Then the battery will perform almost like it would if it had a 100%SOC. You can do around 12-14 cycles of the 50% to 90% SOC rates but will have to perform a full 100%SOC after that to keep from doing damage to your batteries.

When charging with the higher DC Voltage the battery will draw the proper amount of DC current to complete its charge cycle. Then it rest back to 12.6VDC showing you it is at a 100% SOC. Your battery will usually rest at full charge of 12.6-12.7VDC after being charged at 14.4VDC and 13.6VDC for three hours...

Something like this at any rate haha..
Roy Ken

PinkLeopard wrote:
Replaced 2-6 volt house batteries because they weren't holding a charge. Immediately afterwards voltage dropped rapidly to about 12.8. Checked water - it's ok. Charged with generator and shore power to 13.6 but they're not holding a charge.

Posted By: PinkLeopard on 05/09/14 09:20am

Aren't you supposed to be able to charge them up to 14+ and when it shows around 12.5 you're supposed to charge them.

I think you don't understand how this works. When the batteries are being charged, the charging device (generator, converter, charger) will indeed put out 14+ volts to the batteries. However, once the batteries get to a full charge (12.6 to 12.8v) the charging device will reduce the charging output to about 13.4 volts and will keep the batteries fully charged.

Once the charging device is removed from the batteries, the batteries will continue to hold their "full" charge of 12.6 to 12.8 volts. Once a load in applied, the batteries will discharge slowly....depending on how much load is applied.

So in your case, when the batteries are disconnected from the charging device and no load is applied to them, 12.8 volts is normal!

Hope this helps

Ron

Let's not overlook the fact that automotive battery charging systems are a LOT more simplistic that the average battery charger. The automotive system NEVER tapers the charge as the battery reaches a FULL SOC. It can't, the SOC of battery that's being "charged" cannot be sensed due to varying electrical loads in parallel. So a compromise MAXIMUM "charging" voltage is used as the target alternator/VR voltage output,

That results in a maximum SOC of the chassis battery being only 60-70%

Only a charger that operates with no parallel loads can sense a battery's TRUE SOC.

Reading the various posts on the subject makes it fairly obvious that something strange is happening when two 6 volts batteries are used in series as house batteries coupled with a single 12 volt chassis battery.

1. Electrolyte boils away in the 2 six volt batteries when being charged "underway" by engine alternator.

2. OP describes 2nd instance.

Guessing....

Temperature difference due to differing location? Warm/HOT chassis battery in the engine compartment vs house batteries at OAT, plus more cooling for house batteries.

When I rapid charge a 12 volt battery I have often noticed the 4 battery "interior" cell's electrolyte bubbling when the 2 battery end cells do not.

I have attributed this to the end cells receiving more cooling.

Two 6 volt batteries have a total of FOUR end cells being cooled by OAT...

It is well known that "flooded" lead-acid battery SOC, FULL SOC terminal voltage rises with declining ambient temperatures. Therefore ALL automotive VR's have an internal thermistor that is used to sense OAT and adjust the alternator charging voltage accordingly.

"WARM" VR/chassis battery, SOC (FULL) = 12.8. "COOL" house battery requires a higher charging source voltage (13.2?) in order to reach FULL SOC....

????

ell