AGM Battery maintenance/charging for dummies?

[Arya Ebrahimi]

Ok, so I have a Diehard Platinum Marine battery in my camping trailer. I also have a couple of old Optima Red Tops laying around that I'm hoping to revive by parallel charging with a good battery per Optima's website instructions.

I do not have the requisite degree in AGM batteries that seems to be necessary in order to charge/maintain these batteries. Can someone please dumb it down for me and just tell me how I can cheaply/effectively keep this battery topped off without going into the inner workings and chemistry of batteries? I've read a lot about these batteries and I think I understand some of the principles, but it seems like these batteries use relatively new technology and there isn't a lot of good "consumer friendly" info on how to maintain them.

Typically I try to learn the ins and outs of everything I put my hands on, but chemistry has always been my downfall and I'm drawing the line with these damn batteries.

For reference, I do have a large old school battery charger(the kind that is about the size of a carry on bag and has its own wheels) that has 2A/10A charging modes. Can I use this thing?

Thanks in advance for your help!

[BillTex]

For AGM's you really should use a better grade 3 stage charger as they need a higher voltage to reach their max capacity.

Try this for more info http://www.marxrv.com/12volt/12volt.htm

[LandCruiserPhil]

Great link ^^^^^^

[Arya Ebrahimi]

Can you recommend me a good 3 stage charger? I don't want to break the bank, but I generally buy quality and subscribe to the "I'm not rich enough to buy junk" train of thought.

[nuclearlemon]

i've never had to do the jumper with a lead battery thing for my reds...i've got a battery tender jr, which is rated for agm batteries and i just trickle charge them. i also "condition" batteries now that i heard they should be. we'll see if that makes a difference with the blues in my 80. the trickle charge thing gave me great life out of reds tho. i hit 10 years with the one in my 40 and i've got two more that are six+ years old, although not in running rigs anymore.

[dwh]

In a nutshell, here is the difference between an FLA (flooded lead-acid) battery, and an AGM (absorbed glass mat battery):

One has fiberglass matting between the lead plates and doesn't slosh.

That is all. Carry on.




In other words. What works for one, will work for the other.

So...yes, you can use your plain ol' automotive benchtop charger on an AGM battery. And...no, it won't get it fully charged. But...it won't get a flooded battery fully charged either. So...no difference there.


With any lead-acid battery (FLA, AGM or GEL), to get it fully charged, you have to let it soak up power until it can't soak up any more. At that point, the chemistry is said to be, "fully absorbed".

To get it really done right, you need to pump it up with "a bit of the old ultra-voltage" (yea, I liked A Clockwork Orange). For most FLAs and AGMs, that means taking it up to some higher than normal voltage and holding it there a while.

That's what a multi-stage charger does.

A 3-stage charger will do a "bulk stage" by raising the battery's voltage to (usually for most chargers) 14.4v, and then do an "absorb stage" by dropping the voltage to 14.2v and holding it there for a few hours, and then drop to "float stage" at something like 13.6v just to keep the battery from self-draining as it sits around.

That's pretty much the routine that all battery manufacturers recommend for both AGM and FLA batteries.

There are of course, a few exceptions to the rule. Interstate as I recall has one flooded battery that they recommend taking up to an unholy 15.8v (as if there is actually a charger on the market that can do that...).

But for the most part all AGMs and FLAs recommend the 14.4v/14.2v/13.6v 3-stage charge routine.


(GELs are different. They are like the females in the battery world. They are sensitive and must be treated with more care than AGMs and FLAs. They like a slightly lower voltage and don't you DARE go too high.)

[takesiteasy]

To get it really done right, you need to pump it up with "a bit of the old ultra-voltage" (yea, I liked A Clockwork Orange). For most FLAs and AGMs, that means taking it up to some higher than normal voltage and holding it there a while.

So here is a twist on this question. I have a dual battery setup in my Tacoma with the IBS separator system. Most of the time, both batteries are being charged by the alternator. I intended to use a Battery Tender Plus (3- stage) to condition the camper battery from time to time ( it is a Sears Diehard Marine- AGM). The charger is wired directly into the camper power circuit and set up to charge the battery from shore power. What I found out is that the IBS connects both batteries when it senses the charging current, so the Battery Minder is trying to charge both batteries at the same time. I have read that it is not a good idea to try to charge both a flooded battery and an AGM at the same time from a single charger as one battery will likely reach the target threshhold before the other one so one battery (probably the camper battery) is not going to get fully conditioned. I suppose the obvious solution is to install a battery disconnect switch under the hood to manually isolate the camper battery for charging. But this is not the most convenient solution. Anyone have any other ideas about this?

[dwh]

So here is a twist on this question. I have a dual battery setup in my Tacoma with the IBS separator system. Most of the time, both batteries are being charged by the alternator. I intended to use a Battery Minder Plus (3- stage) to condition the camper battery from time to time ( it is a Sears Diehard Marine- AGM). The charger is wired directly into the camper power circuit and set up to charge the battery from shore power. What I found out is that the IBS connects both batteries when it senses the charging current, so the Battery Minder is trying to charge both batteries at the same time. I have read that it is not a good idea to try to charge both a flooded battery and an AGM at the same time from a single charger as one battery will likely reach the target threshhold before the other one so one battery (probably the camper battery) is not going to get fully conditioned. I suppose the obvious solution is to install a battery disconnect switch under the hood to manually isolate the camper battery for charging. But this is not the most convenient solution. Anyone have any other ideas about this?

Yea. That's a good question.

Technically, it's not recommended to charge two different batteries at the same time - or even two identical batteries with differing states of charge - with a 3-stage charger.

The reason has nothing to do with conditioning:

It's that if there is an absorb stage, then the charger is going to hold the higher absorb stage voltage for however long it takes for the battery with the lower charge to reach fully absorbed. Since the other battery will have reached fully absorbed sooner, it will end up being held at an elevated voltage for too long and be overcharged.

This has nothing whatsoever to do with the fact that one battery has fiberglass fabric between the plates and the other doesn't.

This problem will happen with any two batteries - even identical batteries - if one is at a lower state of charge, or is a little older, or a different type, or brand, or size or blah, blah, blah. Whatever.

That's why, for charging two different batteries at the same time, you want to use either a constant voltage charger (like an alternator/voltage regulator, or a benchtop charger), or a 2-stage charger, which just bulks until both batteries hit 14.4v and then drops to float and omits the absorb stage completely.


The real question is: Why, does Battery MINDer (who make both 2-stage and 3-stage chargers and know what they are doing), say that you can hook up multiple batteries to their 3-stage charger?

I think, they've got a timer on the absorb stage, and so their little 8a charger isn't going to do any real damage by having one battery being in absorb for an extra little while and eventually the timer will kick it out of absorb anyway.

[Arya Ebrahimi]

So where does one go to shop for battery chargers since no specific recommendations have been made?

The only place I've seen that advertises them is West Marine and they are $$$.

[dwh]

Oh. And I wouldn't have any problem at all with using the Battery MINDer (which is not the same as Battery Tender) charger and letting the IBS tie the batteries during shore power charging.

Even if the batteries were one flooded and one AGM. Or even different sizes.

But that's the Battery MINDer - I wouldn't do it with any *other* 3-stage charger.

The little 8a charger will get them both fully topped off and then float them. And, who knows...the "de-sulphation" might actually be good for the batteries.

(No one seems to really know if de-sulphation pulses actually help a battery, and every manufacturer of de-sulphators does it a little differently - but they all claim their way works.)