AGM Overcharging?

[jonyjoe101]

When the battery gets drained to 10.1 it won't last long, even if its a deep cycle. For agm to extend its life you shouldnt go below 12.1 (50 percent) at 11.5 volts your at 10 percent which is the safest you can drain any lead acid.

I owned my agm for about 3 years, rarely took it below 12 volts, recently I got it below 11 volts about 3 times and thats all it took. It still charges up, and it reads 12.9 after charging all day but it has very little capacity. It drains quickly when I put loads on it.

If you could connect a dc wattmeter to your aux battery you could see how many amps are going into your battery during charging. dc wattmeter can handle up to 60 amps, you might not be getting a good charge and then draining it to low.



soc

 

[classic72]

Ok, will check out the watt meter. Thanks so much!

 

[dwh]

They make those watt meters in a bunch of different ratings, even 100, 130, 150 amps:

https://www.amazon.com/dc-watt-meter/s?ie=UTF8&page=1&rh=i:aps,k:dc watt meter

 

[dwh]

It still charges up, and it reads 12.9 after charging all day but it has very little capacity. It drains quickly when I put loads on it.

Yea, true dat.

A toasted battery can sometimes seem to behave normally. It'll charge up and have a normal resting voltage, but might only be good for a few amp*hours before it's dead agaIn.

When they're that bad, they won't usually hold full charge voltage very long. Just sitting around the voltage drops pretty quick.

 

[classic72]

I was finally able to duplicate it after around 4 days of around town driving with no draw to deplete the battery. I opened my topper and could hear it gurgling. Battery was super hot... IR Thermometer registered 206.8F. I have since pulled the battery out of the ArkPak.

I am now on the hunt for a new battery BUT my question is do I need to match my starter battery to the battery in the Arkpak by both size and type, by only type, or does it matter at all? My factory battery is a Group 65. I honestly don't want to change from that but if I get a matching Group 65 it looks like it may be slighter wider than the Arkpak. All other dimensions fit. Ideally I want to get a Hybrid AGM with Group 65 under the hood and Group 31 in the Arkpak but is that ok? Specs between the group sizes are different. Everything I have read is mixed opinion... curious about real world experience.

All this is for running a fridge... makes me think I should just sell the fridge and get a $40 Coleman Xtreme, lol.

 

[e60ral]

Have you verified the voltage your ArkPak sees? It shouldn't need to be the same kind of battery. What charging voltage does your battery want and what is it getting?

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[classic72]

I didn't think I needed to match type to type (e.g. Lead Acid Starting and AGM Deep Cycle) but everything I am reading on that front is says yes... AGM to AGM or Lead Acid to Lead Acid. Don't mix and match. It appears now that Group Size doesn't matter as much as the Chemistry.

 

[e60ral]

I didn't think I needed to match type to type (e.g. Lead Acid Starting and AGM Deep Cycle) but everything I am reading on that front is says yes... AGM to AGM or Lead Acid to Lead Acid. Don't mix and match. It appears now that Group Size doesn't matter as much as the Chemistry.

It only needs to match of they are not isolated

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[dwh]

I didn't think I needed to match type to type (e.g. Lead Acid Starting and AGM Deep Cycle) but everything I am reading on that front is says yes... AGM to AGM or Lead Acid to Lead Acid. Don't mix and match. It appears now that Group Size doesn't matter as much as the Chemistry.

Read this thread:

http://forum.expeditionportal.com/threads/171723-AGM-vs-Lead-Acid-for-solar-(in-2017)

In paricular, look at the pics of the Deka Intimidator battery the guy bought. Notice how on the label, it specifies acceptable voltage ranges for charging and floating, not pinpoint precise voltages, because lead-acid batteries aren't precise electronuc components - they are chemistry experiments in a plastic box.

AGM is lead-acid. The chemistry is the same.

It is very important that batteries be the same type, size, age, brand, etc. when they are tied into a full-time permanent battery bank. It's not important when they are only tied during charging.


If your truck came with a flooded battery under the hood and you replaced it with an AGM, *how* would you tell the voltage regulator to change its behavior? You wouldn't. You can't.

Yet manufacturers sell AGM cranking batteries and don't issue warnings that "the chemistry is different so you must change your voltage regulator".

Because it doesn't matter. Except for a very few special cases, all lead-acid batteries operate in the same voltage range, because they are basically all the same chemistry experiment with minor differences.


I think Verk nailed it. Sounds like the battery is internally shorted.

 

[classic72]

Great post... thanks for the link. Now it makes sense.

 

[dwh]

Rereading that thread, I see I should have mentioned that sealed lead-acid (SLA) and valve-regulated lead-acid (VRLA) are the same thing. All SLAs have blow-off valves and are thus VRLA.

I don't much like the VRLA designation. There is more than enough confusion around the subject of batteries to begin with; using the word "regulated" to mean both voltage and/or pressure is technically correct, but it's clunky and just adds further to the confusion.

 

[classic72]

Do you see any issues going with just a regular Deka 31 Marine Deep Cycle rather than a AGM or Gel Equivalent in the bed of the truck with a topper? I am much less concerned with service life and if I can get a 2-3 years out of it I would be happy for the less money spent. Again, since I am only running a fridge I am looking at ROI and quite honestly the Flooded is about $250 less than the AGM. It would be encased in the ArkPak and mounted upright then bolted down... no different than under the hood of a vehicle.

It is in my Daily Driver so really would not sit long without charging ever however would only have a discharge on it once or twice a month when the fridge is in the truck during an outing.

 

[rossvtaylor]

You're getting great info and these guys know their stuff. I love reading everything they write... especially the descriptive "chemistry set in a box."

I'm jumping in only because of the mention (above) of a gel battery option. With flooded lead acid (your "normal" battery style) or absorbed glass mat (the "spill proof" style) they are both plates and an acid solution. The only difference is that the AGM battery holds the solution in almost-fully-saturated fiberglass mats, sort of a like a sponge. But, the solution is still a liquid.

With a gel battery, the solution is gelled by adding a silica component (or something magic). It really is like a gelatin. And, there's the complication... With the other batteries, overcharging can hurt them but they can survive. With a gel battery, a single overcharge can really damage it. When overcharged (either too high or too fast), the offgassing can create a bubble pocket between the plate and the gel. That pocket means the electrolyte gel solution isn't in contact with the plate any longer and that area is then unable to react chemically... meaning, it's not longer helping the battery be a battery.

FLA or AGM are good options. But I'd stay away from gel varieties in our uses.

 

[dwh]

Do you see any issues going with just a regular Deka 31 Marine Deep Cycle rather than a AGM or Gel Equivalent in the bed of the truck with a topper?

The issue is venting.

During charging, electrons come into contact with water molecules in the electrolyte solution (diluted sulfuric acid) and cause some of the water molecules to "let go" their molecular binding, separating into hydrogen and oxygen, both of which form bubbles and float to the top.

With a vented open cell battery (removable caps), that hydrogen and oxygen (rocket fuel) vent out into the atmosphere.

With a sealed battery, it retains the gasses which then mostly recombine into water.

Sealed (SLA/VRLA) have spring-loaded pressure relief valves. Under normal use pressure does build up over time (not all of the gasses recombine into water) and a tiny amount of gasses gets vented now and again. Not much. When overcharged they can vent quite a lot. As you've seen, they can also vent quite a lot if the battery shorts internally and overheats.

So best practice, safety first, CYA recommendations are to always provide a sealed box with a way for the gasses to vent to a bigger atmosphere if the batteries are installed in a closed area.

This is often ignored for sealed batteries in an enclosed area since they don't vent enough to matter unless something goes wrong.

But open cell batteries release explosive gasses constantly while being charged. There are those who will argue that the bed topper isn't sealed all that well and the rocket fuel being released into that area isn't all that much, so a sealed box with a vent tube isn't really needed in that situation.

In today's litigous society, you will never catch me publically advocating such a shocking breach of safety rules.



But you would not catch me doing it in real life either. If I was going to install a vented battery into a truck bed with a topper, I would indeed use a sealed box with a vent tube (going up - the gssses are lighter than air) that directs any rocket fuel to the outside.

Also, vented batteries have been known to explode when sparks come too close during the rocket fuel production and venting process, so that's another reason to use a sealed box - cleaning up the mess would be more trouble than doing it right to begin with.