AGM batteries

[Mike S]

I bought my '77 Argosy strictly for boondocking.

I plan on building a drawer/tray in the space under the wardrobe in the rear bath, and installing 2 Deka 8AGC2 6V AGM batteries in series to give me 220 AH at 12V.

I have searched around but not found an answer to the question of whether the factory installed Univolt will properly charge and maintain these AGM batteries?

I could buy a better 3 stage battery charger/maintainer and wire it into the system, leaving the Univolt as a converter only to power the 12V when running a genset. I would prefer not to do this unless needed.

Any ideas or experience with this?

Thanks.

Mike

[richinny]

just a thought......
is putting all that weight back there ok?

[Mike S]

It is 68 lbs/battery, plus cabling. Probably less than 150 lbs total. I don't know is this is feasible, but I would remove the existing battery, so that would factor into the balance issue.

M

[bryanl]

The converter might do OK for the AGM's, just make sure the charge voltages, float especially, are within specs for the AGM batteries. If it is an OEM 1977 converter it will be a heavy thing that is essentially a current limited fixed voltage charger. That means it can take a while to get a battery properly charged.

Theoretically (by code) the AGM's require a vented battery compartment, just like wet cells. That raises the question of why the extra expense for the AGM's - but a lot of folks put AGM's in 'innapropriate' spots (me included!)

There is also a question of why a pair of 6v rather than a pair of 12v. That 'debate' often gets awfully rank and a lot of folks spend unnecessary money seeking benefits that don't exist.

What limits the lifespan of most RV batteries is a lack of attention to proper charging and storage management. See Basic battery guidelines for some ideas on this.

[Mexray]

AGM's will only tolerate up to about 14.2 volts during charging...higher voltages will 'boil' the stationary electrolyte away from the plates causing battery failure...note: this type of failure won't be covered by the warranty...

Your original Univolt will probably put out voltages higher than 14.2 volts if the batteries are highly discharged...and you will ruin them.

Get a 3 stage charger!!! This will be the only way to protect you new, high priced, AGM batteries!

You can get a modern, solid state type converter/charger from suppliers such as BEST CONVERTER for around $200. It's hard to believe how much better your battery bank will perform, and how much more 'idiot proof' you system will be with a modern charger!

You batteries will be recharged faster, with a proper 'finishing' charge and then switched to a 'float' setting to ensure they aren't overcharged...try one, you'll like it, and the money spent is much less that replacing a set of AGM's that have been damaged by an old Univolt!

That was one of the first things I upgraded on our 78 Ambassador...an easy job.

[68 Overlander]

Hi Mike
I strongly recommend that you do not charge AGMs with the Univolt. I can tell you from experience and hundreds of real life testimonials that they don't play well together. You mentioned 3 stage and that is the only way for any battery in our opinion. The benifits are endless. I'm not up on Deka because they aren't that popular in the industry but do look at their website for recommend charging parameters. I can tell you not to read too far into it because they don't keep up with the times most often and AGM is pretty forgiving as long as you have multi-stage capability.
As for using it as a power supply, maybe it would be okay except the Univolt needs a battery to act as a filter and without it you will see a lot of voltage spikes and surges to your accessories. Not good. They used to offer a battery emulator for this very reason for people that used Airstreams in a permanent location therfore not needing a battery for towing or dry camping.

[lewster]

BTW,

Here are the charging requirements from the Lifeline web site.

3 Stage Chargers
Bulk 14.2 - 14.4 volts
Acceptance 14.2 - 14.4 volts
Float 13.2 - 13.3 volts


2 Stage Charger
Bulk 14.2 - 14.4 volts
Float 13.2 - 13.3 volts


Single Stage Charger
Bulk 14.2 - 14.4 volts
Once the battery is fully charged, remove it from charger.

[rp709]

I am using two 6 volt golf cart batteries in series and a 3-stage battery charger. I want to add an AGM battery eleswhere in the coach. I have heard conflicting info about the compatability of lead acid batteries and AGM's in parallel. Ron

[bryanl]

I have heard conflicting info about the compatability of lead acid batteries and AGM's in parallel

The general rule is that all batteries in a bank should be as similar as possible - down to manufacturer, battery model, and even age.

AGM batteries are lead acid batteries - which is a similarity - but they are quite a bit different from the wet cell type. The differing characteristics such as internal resistance will likely create significant imbalances in charging and use.

To some extent this difference is reduced by the damping effect of wiring as the batteries are physically separate but that distance also has its downsides.

What the rule means is that the more difference there is between batteries in a bank, the less satisfactory the performance becomes. This gets to where there isn't any benefit to having the batteries in a bank on down to where there is degradation of capability. What impact a difference will make depends upon many things besides the batteries.

[68 Overlander]

I agree with Bryan. The similarity is that they are both 12 volt banks and lead acid and will charge and discharge together but probably at a price, early failure of one or both.

[Mexray]

What's important is that all the individual cells in a battery bank should be of equal size (and age).

If you mix different sized batteries, their cells will be of different size as well, and discharge/charge rates will differ, causing some to under-perform and not reach a full charge, accelerating the formation of sulfate on the plates...and shortening their useful life in your RV.

AGMs and Flooded Cell batteries also should not be mixed in one battery bank...their ability to accept a charge is different, and you will experience shorter service life.

[rp709]

Why not make two separate battery banks with a battery selector. That way you have independant sources of power and can charge them separately, as necessary? Has anyone done this? Ron

[Mexray]

We do just that when we boondock where you can't run a generator at night...

I made a harness with a 175 amp connector that's mounted to one of our two Gr 27 batteries in the AS.

I have a matching plug with a longer harness (#2 awg size cables) that will reach into the rear of our tow rig where I stow three more Gr 27's hooked in parallel.

I also have a 1500 watt inverter mounted with the extra batteries so I can plug in the AS's shore power cord to power the AC circuit to the TV, Sat receiver, or DVD player. I turn off the AC breaker at the AS's panel that powers the converter/charger, and of course the Air Cond's breaker as well.

In the morning, I can power up the generator, plug the AS power cord in, flip on the breakers, and use the converter/charger to recharge the battery bank...works great!

[lewster]

Originally Posted by rp709

Why not make two separate battery banks with a battery selector. That way you have independant sources of power and can charge them separately, as necessary? Has anyone done this? Ron

I 'sort of' do that now. I have a complete 2-panel 200 watt AM Solar charging system in my Sprinter van, along with 2 Lifeline GPL-6CT 300 amp/hour golf cart batteries and a 2000 watt sine wave inverter/charger.

The inverter feeds a water-proof 120VAC outlet at the bumper so I can plug in the trailer's 30 amp cord right to the truck when I need extra 'juice'. It will also charge the trailer's batteries as it will run the converter.

Next up is a direct 12VDC connection, but that's a little more involved and will require some 4/0 cabling to avoid any voltage drop in the 12VDC lines.

I'll post a few shots of the set-up when I reach OR and empty out the van. It's a little difficult to do that now while fully packed and on the road.

[bryanl]

What's important is that all the individual cells in a battery bank should be of equal size (and age).

I haven't seen this criterion before. It doesn't fit as a major concern with what else I have seen or my experience.

Why not make two separate battery banks with a battery selector.

you loose effective capacity. I'd refer you to my explanation but I see some here who blew a fuse on my attempts to explain the phenomena. So check Splitting battery banks for a more direct calculation.