AGM Battery Suggestions - Good, Better, Best?

Vulcan Rider wrote:
I'm not quite convinced that they are really worth the extra price in a heavy duty, deep cycle application, versus good quality deep cycle wet batteries that is.

Can't really argue that, but after 10 years of watering FLAs, that alone is worth the cost to me.

scrubjaysnest wrote:

The quick answer is for the Surrette 12 volt AGM, 14.7 volts charge and 13.65 volts float at 77 deg F
The long answer is a chart of current and voltage over time.

A really lot of good information there but WAY more than the average battery user really needs to know.

If you can't quite attain the "bulk" charging voltage, that is NOT a problem; it just takes longer to charge. Assuming that you apply the lower voltage long enough, you end up in the same place.

I am a BIG fan of AGM batteries in vehicle use: cars, motorcycles, tractors and lawn mowers even. But I'm not quite convinced that they are really worth the extra price in a heavy duty, deep cycle application, versus good quality deep cycle wet batteries that is.

KenMast wrote:
Hi scrubjaysnest,

Thanks for your comment. I'm a novice when it comes to RV batteries and I don't really know what you mean. Would you be so kind as to go into further details. I assume that the batteries would charge the same as my current battery does. What am I missing? Thanks a lot for any more information that you can provide.

Ken

The quick answer is for the Surrette 12 volt AGM, 14.7 volts charge and 13.65 volts float at 77 deg F
The long answer is a chart of current and voltage over time.
One has to go the manufacture's web of a given battery to get specific charging specs.
My Exides are 14.5 volts boost or bulk charge and all the current the battery will take up to 5 X c/20 rate; or c=105AH there for 5*105/20 = 26.25 amps. That covers the first 80%. Absorb gets the next 20%; volts is raised to 14.9 and held there until current drops to about 1 amp at which time you shift to float or 13.3 volts.

The only two converters that come close are the Iota and Progressive Dynamics and they aren't very close. Iota with the IQ4 pendant is 14.5 volts boost for an hour then drops to 13.6 volts for absorb if I remember correctly. Some of the PD models have a manual over ride that lets you keep boost going longer. But their absorb voltage isn't high enough either. Forget the WFCO converters, some folks have apparently tricked the WFCO's into boost by having two or more batteries, run them down below 50% state of charge and turn on every 12 volt appliance in the camper. Never worked for me.

The above is if you want to get maximum life out of the batteries. A quality flooded or AGM properly maintained has an expected life of 6 to 10 years.

Each battery maker has different requirements to maximize battery life. But ball park is 14.5 volts boost or bulk charge; 14.8 volts absorb charge and 13.4 volts for float. AGM's don't require equalizing but flooded lead acid do and that voltage 15.0 or higher.

Check out batteryfaq.org for detailed answers. The site is updated about every 6 months. Another good source is solar-electric.com in their faq section. They are also a vender. Their forums section has a lot of good information on solar projects, grid tie, off grid and RV.

Good= UPG, Diehard, Interstate
Better= Trojan, Enersys Pure, LIfeline
Best= Concorde, Rolls/Surette, some telecom batteries that are exorbitantly expensive

Most of these AGM mfgs. have specific charging guidelines and you can match your charging system with that to see if things mate. I have two banks of batteries, one with flooded wet cell 6V's and one of AGM batteries. I charge both banks simultaneously with one solar controller set to voltages that are good for both.

scrubjaysnest wrote:
How do you plan to charge them? Your converter won't do the job right and that is a lot of money to spend and not protect them by proper charging.

The nominal and float voltages for AGM are about .4 V higher than a wet cell type. Nominal=12.9 to 13; float 13.2 to 13.4.

You can't really make that statement without knowing what voltages his specific converter applies to the batteries.

AGMs tend to charge a bit faster but a wet cell charging voltage might leave them around 95% instead of 100. That's not a big deal as AGM chemistry does not suffer from sulphation much and never charging above 95% really does no harm.

In my unit, the generator and shore power charging isn't too high but when the engine is fired up going down the road, the charging voltage is more than enough to bring them to to totally full.

It is nice to know what is going on with the charging but normally NOT necessary to fret over the relatively minor difference.

Hi scrubjaysnest,

Thanks for your comment. I'm a novice when it comes to RV batteries and I don't really know what you mean. Would you be so kind as to go into further details. I assume that the batteries would charge the same as my current battery does. What am I missing? Thanks a lot for any more information that you can provide.

Ken

Lifeline
Fill River

i have these CD technologies





weigh 100 pounds each
139 AmpHrs at 20hr rate

How do you plan to charge them? Your converter won't do the job right and that is a lot of money to spend and not protect them by proper charging.
As mentioned Surrette are the best. Be careful at NAPA some of the GC-2s appear to be AGM's but are actually flooded lead acid

I got the following 2 years ago and have been very happy:

House battery - Optima 8052-161 Blue Top group 31
Engine battery - Optima 8025-160 Red Top group 25

Good= cheaper
Better = middle
Best = Surrette brand

My 12v 80ah Lifelines are very good. Only maintenance is dusting.