AGM charging requirements

[Five Wood]

I have two 12volt deep cycle wet cell batteries that I want to replace with 2 12volt AGM batteries. I believe my present converter/charger will be sufficient to charge them with. I’ve been unable to make contact with Progressive Dynamics to ask the question. Any thoughts here?

 I’ve attached a picture of the present batteries and charger. 

[Kirk W]

When charging a wet cell battery compared to an AGM battery, the key difference is that AGM batteries require a more controlled charging process with a lower voltage due to their lower internal resistance, meaning they can accept higher charging currents without overheating, while wet cell batteries typically need a higher voltage to charge properly but with a lower current.

[D&J]

I used the same converter but the 60 amp version on my AGM batteries for years and would still be using it but I changed to lithium batteries.

Denny

[Lou Schneider]

If you charge lead acid batteries at too high of a voltage, the electrolyte "boils" as the water in the electrolyte separates into it's component hydrogen and oxygen molecules and is lost.

AGM stands for Absorbed Glass Mat.  AGM batteries are lead acid batteries where the electrolyte is suspended in a sponge-like glass mat between the positive and negative plates.  There's no way to replace any consumed water so the charging voltage has to be kept below the point where the water electrolyzes.  Generally this means charging at 13.6 volts or less for a 12 volt battery.

The problem is the Charge Wizard technology in this converter increases the voltage to 14.4 volts for faster charging when it is first turned on or if it senses low battery voltage.   This lasts until the output current reduces to a pre-set value, then the converter returns to 13.6 volts.

Ironically the 14.4 volts this converter puts out during the Charge Wizard's Boost and Desulfation modes makes it a closer match to the charging requirements of a lithium battery than an AGM battery.  Converters designed for lithium batteries simply keep their output at 14.6 volts all the time.  I suggest going with lithium instead of AGM especially since the prices have come down to where many lithium batteries on Amazon are cost competitive or even less expensive than AGMs.
 

Edited November 13 by Lou Schneider

[oldjohnt]

   Good questions Five Wood, welcome aboard. I owned that very same PD Charger (still do as a bench charger) and used it BOTH when I had Flooded Lead Acid and later upgraded to AGM (Absorbed Glass Mat) Deep Cycle batteries in my RV. You asked for any thoughts, so here is my opinion based on personal experience.

 1. For sure it "WORKED" when I switched over to AGM, I never had any problems.

 2. HOWEVER, based on the manual and observation I considered it better suited for wet flooded lead acid FLA over AGM even though it still worked, the ideal charge parameters (Voltage, Current, Time) for AGM are a bit different than FLA. 

3. My AGM's specs warned against any extended charging period of high voltage as can be done using wet flooded lead acid if the charger performs an occasional 4th stage so called equalization or desulfation cycle in addition to the normal 3 stage Bulk Absorption and Float typically used for FLA. I'm ONLY pointing out the difference in ideal charging parameters for AGM and how excess voltage or time may not be best for AGM chemistry..Ive read one should NOT run any equalization or desulfation cycles (high voltage) using AGM's, that's only for FLA

BOTTOM LINE OPINION

 While it will still "WORK" if you change to AGM, its my opinion its NOT the perfect ideal situation. INSTEAD due to the fact LiFePo4 Lithium prices have come down, their features (BMS, Low or High Temp protection, Self Heaters) have improved, less voltage sag as capacity is diminished, can discharge to over 80% as opposed to only 50% with AGM or FLA. What I'm saying is if you're upgrading anyway, you might want to consider going ahead biting the bullet, spending more now, and going to the future instead of older technology. However ONLY YOU your needs and budget can make the choice, none of us. I upgraded from FLA to AGM now Lithium and never going back.

 I'm no expert on this, see what other PD owners, AGM and Lithium owners, and the experts here have to say. Im sticking with your PD will WORK if you change to AGM but I would consider upgrading to Lithium !!!!!!!!

PS In addition to what the fine gents (a good bunch of knowledgeable experts) here have to say, you might take a look at what Will Prowse on You Tube DIY Solar has found !!! 

 

 John T    

 

 

Edited November 14 by oldjohnt

[Lou Schneider]

3 hours ago, oldjohnt said:

PS In addition to what the fine gents (a good bunch of knowledgeable experts) here have to say, you might take a look at what Will Prowse on You Tube DIY Solar has found !!! 

Absolutely take a look at Will Prowse's DIY Solar videos and his website.   He does a fantastic job of presenting things in a clear, easy to understand manner.

[D&J]

That Progressive converter drops off to 13.2 volts after the batteries are charged not 13.6 that is perfect for lead acid batteries that are 2.2 volts per cell fully charged, I checked mine with a digital meters many times over the years. My last set of AGM batteries lasted 8 years on that charger and they weren't bad when I replaced them they lost capacity from use. That charger is not made for lithium batteries because if their charging profile and higher resting voltage after charging.

Denny

[GlennWest]

Lithium batteries and AGM are very competitive in price now. Just saying. 

[D&J]

3 hours ago, GlennWest said:

Lithium batteries and AGM are very competitive in price now. Just saying. 

That's why I changed to lithium, the biggest added expense was the new converter and DC to DC charged to increase the voltage from the truck when going down the road, we run our residential refrigerator and freezer when going down the road so I want to keep the batteries up. I would never go back to any kind of lead acid battery after having lithium.

Denny

[oldjohnt]

15 hours ago, GlennWest said:

Lithium batteries and AGM are very competitive in price now. Just saying. 

Its getting closer all the time !!!!!!!!!!! over 54 years I went from FLA to Deep Cycle FLA to AGM to Lithium AND NEVER GOING BACK LOL   Im running SOK Lithium working great no problems but if I were to start all over Id go with Epoch lithium Batteries, just sayin

John T

[Five Wood]

Thank you all for the responses. I’m going to go with the AGM’s. I appreciate the help. 
 

Jim

[oldjohnt]

53 minutes ago, Five Wood said:

Thank you all for the responses. I’m going to go with the AGM’s. I appreciate the help.

You're welcome, There are several good quality brands of AGM's out there, I charged my AGM's using that Converter/Charger. When you connect two new identical 12 Volt AGM's in parallel (still 12 Volts) the Amp Hours of energy storage capacity doubles. Of course, its best if the two batteries are identical in age, brand, rating, and specs. 

PS I forget if that charger has or allows for any adjustments or modifications in its charging profile for AGM versus FLA ???? CHECK THE MANUAL but I DO NOT advise the use of any so called Equalization or Desulfation type cycles (some call a 4th higher voltage short term stage) for AGM batteries..............  

John T

Edited November 14 by oldjohnt