# and Type of house batteries

Hi pnichols,

You could be right in that it was simply a failure to one lead acid cell, creating the same issue with both pairs of batteries.

Our rig locates the battery compartment just forward of the rear axle. It could be that might jar the batteries more than a typical motor home. But our rig is an E350 with suspension upgrades. I have always considered the quality of ride fairly decent. Who really knows the cause for an assumed cell gone bad with both pairs?

Don't worry about me torching our motor home with excess batteries. Now that I switched to two 6V AGM batteries, I am very satisfied, and my wife Irene is too. I did have to make a slight modification to the battery compartment SEEN HERE, eliminating the raised ball-bearing roll-out battery tray to gain height clearance for the taller 6Vs. The 12V tray dimensions didn't fit the 6V size anyway so it was no great sacrifice.

If you are the least bit curious what I did to make the switch from 12V to 6V, CLICK HERE to read and see some pictures. The installation of 6Vs made it so that I would have to disconnect them and remove them individually to check fluid levels. That was another primary reason for going with AGMs.....install them and forget about them until it's time to replace them.

Ron, FWIW the high resistance open failures I've experience in the past in my liquid acid vehicle batteries had nothing to do with balancing (since they were single starting batteries) or probably my charging method (stock engine alternators).

It must have been just plain early failures from internal corrosion or normal vehicle g-force vibration. AGM should eliminate the g-force issues. I don't know if AGM batteries would be any less resistant to internal corrosion failures than liquid acid.

Just for good measure, if you ever add two more 6V batteries to run in parallel with your current two 6 volters - make sure that the two banks of series batteries are balance-interconnected between them.

(But if you do add two more - please don't burn down you little Class C with all that stored electrical power on tap. ;) )

BFL13 wrote:
Are you sure you belong on the internet? Far too polite! :)

You just kill me. :)

ron.dittmer wrote:
Interesting comments BFL13 and pnichols. Though I highly doubt it, I cannot prove that my charging method did not contribute to my two pairs of 12V lead acid battery troubles. Does innocent until proven guilty apply here? Ha ha.

One thing we seem to agree on.........AGMs are worth the extra expense, whether two-12V/parallel or two-6V/series. They seem to take abuse much better.

Are you sure you belong on the internet? Far too polite! :)

AGMs are good until they aren't, same as other batteries.

Big thing is to have an ammeter (I use my Trimetric) to know they are down to 0.5 amps per 100AH at 14.4 volts before dropping them to spec Float voltage on a recharge to "full".

If your charger won't hold 14.4 that long, like most converters won't, then you will pay the price eventually, and if you don't have a DC ammeter either, you will not be able to tell they are full, so likely leave them undercharged and sulphating.

It's only money, and you will have to get new batteries every so often anyway, so it is just about when, really.

Interesting comments BFL13 and pnichols. Though I highly doubt it, I cannot prove that my charging method did not contribute to my two pairs of 12V lead acid battery troubles. Does innocent until proven guilty apply here? Ha ha.

One thing we seem to agree on.........AGMs are worth the extra expense, whether two-12V/parallel or two-6V/series. They seem to take abuse much better.

ron.dittmer wrote:
I should have made it clear in my reply that when one 12v battery slips in performance, my smart charger kept trying to get the pair to a full charge but could not. My smart charger would not give up and shut off.
The weak battery pulled down the pair, over charging the good one causing boil overs to both.

On my work bench with batteries separated, my smart charger completed the charge to the good battery and stopped. The ill battery would not accept a full charge, causing the charger to keep trying. So when they are back in the motor home together, it is an ill situation.

While on a trip, I would have been better off identifying the weak battery and take it off line and do the trip with just one battery.

The ill situation happened to two sets of 12v batteries, a repeatable condition that has me issuing my warning working with pairs of 12v batteries. If you replace your 12v batteries every other year, you avoid such problems.

Ron ... I think that I agree with BF ... you most likely had a bad cell in the battery that you call the weak battery. This is always possible with any lead acid batteriy - or with any type of batteries for that matter. I've had plenty of good old dry cell flashlight problems due to one battery being bad.

With two 6V RV batteries in series, if a cell goes bad in one battery you no longer have a battery power source for the RV. However as you say, with two 12V RV batteries in parallel, when a cell in one of them goes bad you can "maybe" determine which battery has a bad cell with a voltmeter and then continue camping using only the other good 12V battery. I say "maybe" with regards to a voltmeter determining which battery might be bad, because it is possible (I've had it happen more then once in various vehicles) for a vehicle battery to read on it's terminals a value of "12 volts" - but still not be able to deliver hardly any current at all. I call this a "high resistance current-path-breakdown" ... in which a voltmeter can still read a normal value (voltmeters require very, very little current passing through them read a voltage) but the current path has too much resistance (from corrosion?) to pass any current to speak of.

P.S. The conversation in this thread raised a question in my mind: I wonder if AGM RV batteries - either 6V or 12V - would have less tendency to develop a "bad cell" than liquid acid RV batteries? At least from the perspective of an RV's physical motion and jiggling causing a battery cell structure to fail, it seems that AGM batteries would be less inclined to have a cell go bad than liquid acid batteries.

FWIW, of the three sets of 12V parallel batteries I've had in our RV over the last 12 years: The 1st liquid acid set failed in only 6 months of ownership, the 2nd AGM set never failed but I replaced it after 8 years just in case, and the 3rd AGM set is still doing it's thing. I wish I'd checked the 1st set of liquid acid batteries at least with a voltmeter, but they were on the Winnebago warrantly so I just paid the difference to my RV dealer and had them replaced with the 2nd set which consisted of a pair of 12V 100AH AGM wheelchair batteries.

On recharging, a battery with a bad cell will take more than its share of the current so the other good batteries in parallel are short-changed. So that cannot mean the good battery gets over-charged and spills over. In fact it does not even get full.

Something else must have been going on to make them both spill over. "Overcharging" means battery voltage has gone too high and you will get spill over from the caps (or venting with a sealed battery)

I wonder if the converter in the rig that had the two 12s (twice) had something wrong with it so its voltage went high.

Good that you have solved the problem since then. I just don't think it was from having 12s in parallel as such that was the problem.

I should have made it clear in my reply that when one 12v battery slips in performance, my smart charger kept trying to get the pair to a full charge but could not. My smart charger would not give up and shut off.
The weak battery pulled down the pair, over charging the good one causing boil overs to both.

On my work bench with batteries separated, my smart charger completed the charge to the good battery and stopped. The ill battery would not accept a full charge, causing the charger to keep trying. So when they are back in the motor home together, it is an ill situation.

While on a trip, I would have been better off identifying the weak battery and take it off line and do the trip with just one battery.

The ill situation happened to two sets of 12v batteries, a repeatable condition that has me issuing my warning working with pairs of 12v batteries. If you replace your 12v batteries every other year, you avoid such problems.

Acid boil-over from over-charging is unlikely with a converter/charger with its voltage limited as it is.

A "manual charger" that needs to be shut off by the operator once the battery voltage reaches the desired level could do that if not being watched. The battery voltage keeps on rising into the 16v range or so. But not a converter.

Perhaps what happened there is a battery had a bad cell.

You can parallel two 12s with different AH "sizes" with no problem if they are both in similar condition.(not with a bad cell in one of them) Eg, a 120AH and an 80AH to get a bank of 200AH. Draw them down and at 50% one will be at 60 and the other at 40. They will recharge together reaching 120 and 80 again at the same time. No problem.

Even with good batteries of course you must keep the electrolyte level below the caps so when being recharged and getting warmer from that, there is room under the cap for the expansion, or they will run over.

I found this link regarding balancing, thought it was interesting.

http://www.smartgauge.co.uk/batt_con.html