AGM battery advice

frank33v wrote:

billtex wrote:
As Mark noted, AGM's are great. But anyone planning to invest in them should be sure to install a proper 3 stage charger/converter compatible with AGM charging profile FIRST.
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What would you recommend as a proper 3 stage charger/converter? The one that came with my Northstar says it's three stage but the 3 voltages don't seem to coincide with what Trojan recommends. Trojan recommends absorption at 14.1-14.7 and float at 13.5 for a 12v battery.

If you already have a 3 stage it is likely it is of good quality. However, if you post the name/model we can verify.
If you can research the charging profile even better.
There is some overlap with charging profiles (wet cell/AGM) but most 3 stage C/C are fine for AGM batteries.
Randy at bestconverter.com is the go to Guy for upgrades. Swapping out a C/C is an easy upgrade if you need to.
A proper C/C and AGM batteries are one of the best upgrades you will do.
Set it...forget it.
I like that.
Good luck, Bill

IOTA with IQ controller.

billtex wrote:
As Mark noted, AGM's are great. But anyone planning to invest in them should be sure to install a proper 3 stage charger/converter compatible with AGM charging profile FIRST.
.

What would you recommend as a proper 3 stage charger/converter? The one that came with my Northstar says it's three stage but the 3 voltages don't seem to coincide with what Trojan recommends. Trojan recommends absorption at 14.1-14.7 and float at 13.5 for a 12v battery.

Lifeline all the way. They look like something the military would use.

Lifeline is even bold enough to give a cycle life chart. Taking them down to 50% DoD and they still provide 1000 cycles. That is a long time in camper years unless you full time (and even then it is 3 full years).

I am running two 31XT 125AH 12V Lifelines in a 24V system and they run our compressor fridge, furnace, lights. Wish I had room for a few more.

Ticki2- thanks! Now I get it:)

gitpicker2009 wrote:
ticki2, you may be right, I'm only stating what they told me. When you hook up the batteries in series you double the voltage but the current available remains the same. They say it's 230 amp hours (at 77 degrees) and you divide that by the 20 hour industry rule (where THAT came from, nobody seems to know:)
What part am I missing?

The part you are missing is that you can only use half of the 230ah before recharging , that's 115ah .

Your two 12v are 88ah each but you only have 88ah to use before recharging at the 50% level .

Dennis M M wrote:
Very low internal discharge rate in AGMs which is an advantage if you store for any length of time. I had one in a race car that sat untouched for 2 years plus and then fired right up when I had to move it.

This is good to hear. I have a Mercedes-Benz diesel that sits up for a month at a time. However, with the onboard computer drawing power from the battery - who knows how long the thing (AGM with 900CCA) will last?

gitpicker2009 wrote:
In fact, I think it explains why I boiled off the Interstate batteries in the coach. I was letting the coach, plugged into shore power, charge the batteries, and apparently that's not a good idea, as the "floating" charge point is too high.
thanks again.

Flooded is more tolerant as you can add water. Might be time to review and upgrade your charging system if you are going AGM. AGM can be ruined just as easy.

As Mark noted, AGM's are great. But anyone planning to invest in them should be sure to install a proper 3 stage charger/converter compatible with AGM charging profile FIRST.

We have been running AGM's for...5 yrs?...I would not have it any other way.

...with the the two 12 vdc Interstate batteries -snip- I had 88 ampere/hours.
With the 2 6vdc batteries in series, it's offering 230 ampere/hours--- HUGE increase!

Hmmm... sounds to me like the Interstate rep' didn't do a particularly good job explaining real world battery capacity :(
With your two group 27 batteries in parallel you had a total capacity of ~176 Ah (@ 20hr rate). However, it is generally accepted that you should only discharge to 50% SOC, so that gives you ~88 useable Amp-hours. Two 6V AGM GC2 batteries in series have a (best case) capacity of ~220 A/h (@ 20hr rate), so that's 110 useable Ah.

Yes, 100Ah is more than 88Ah... But without proper charging, you will get neither the rated capacity nor the desired service life from your expensive new AGM's.

gitpicker2009 wrote:
.. I was letting the coach, plugged into shore power, charge the batteries, and apparently that's not a good idea, as the "floating" charge point is too high.

This makes a strong case for you not using AGM batteries. If you "boil off" electrolyte from an AGM it cannot be replaced.

As I asked previously; How do you intend to charge these new batteries??

There are some very good reasons to spend your hard-earned money on AGM batteries, but so far I haven't heard you mention any of them.

Cheers,
-Mark