Do I need AGM specific recharger?

[TerryG]

Just finished setting up my dual battery system. I plan to be out in sub-zero nights for 2-5 days at a time with the expectation of deeply discharging my Optima yellow top at night. I plan to recharge during the day with a 90w solar panel setup, but am not sure this will fully recharge the Optima each day. My expectation is that I will return from these brief adventures with a battery that has been discharged >50% and perhaps not fully recharged each day.

Do I need something like the CTEK Multiuse 7002 to restore the battery to full capacity after I return home?

Thanks ahead of time for the input!

Terry

 

[TerryG]

Sorry but I just found some other threads that answer may question. The answer is "yes" if I want to get the greatest longevity from my batteries.

 

[DiploStrat]

Yes, but ...

Most modern chargers have several stages. Labeled differently by different manufacturers but usually working as follows:

Bulk/Boost: Voltage rising quickly to maximum- Maximum Amperage. From discharged to 80-90% charged.

Absorb/Acceptance: Max Voltage - Declining Amperage. From 80-90% charged to 100% charged.

Float: Decreased Voltage - Minimal Amperage. Holds battery at between 12.7 and 13.x volts.

Some chargers may add a mode called Equalization or Desulphation. (Basically over voltage for a specified period of time.)

Each type of lead acid battery (AGM, Gel, Open) wants slightly different voltages and different times at each of these stages. So you want a charger that can produce the best possible match to the profile recommended by your battery manufacturer. I would always start with the battery manufacturer's recommendation and find a charger that matches. The good news is that many modern chargers have switchable profiles to match many different types of batteries.

Some comments, all based on my experience, and, as always YMMV:

-- As most people do not drive much more than six hours at a time, your engine's alternator is most useful in the bulk/boost stage, and, if large enough and wired properly, can do most of the heavy lifting as long as it runs at something over 14v.

-- Your shore or solar power charger, on the other hand, really needs the right profile, as it is the charger that carries your batteries through the long acceptance stage and monitors the charge rate to determine when the batteries are "fully" charged. As charging voltages vary greatly with temperature, temperature compensation is very nice.

-- Finally, you want to be sure that your solar or shore power charger has a true float, so as not to overcharge your batteries.

Hope this helps to answer you question.

 

[dwh]

Sorry but I just found some other threads that answer may question. The answer is "yes" if I want to get the greatest longevity from my batteries.

Actually, the answer is no. "AGM specific" is marketing hooey. If you look at the recommended charge specs for an Optima, and the recommended charge specs for a Trojan T-105 flooded, you'll see that the exact same charger would work just fine on either one. Obviously, any charger which can do both flooded and AGM *cannot* be "AGM specific".

Further, if you compare the recommended charge profile for an Optima, which is AGM, to an Odyssey, which is also AGM, you'll see that they have different recommendations. So if you bought an "AGM specific" charger that has the perfect charge profile for an Optima, it would not match the perfect charge profile for an Odyssey. How can a charger be "AGM specific" when different AGMs have different charge profiles?

And either the Optima or the Odyssey would be perfectly happy living under the hood of your truck and charging off the voltage-regulated alternator, which is almost certainly not "AGM specific".


With any lead-acid battery, the key is to get the most current into it as you can without overheating it, then let it sit in absorb as long as it takes to get the electrolyte fully saturated, then float it at a voltage high enough to prevent self-discharge, but without being high enough to do damage over a long term.

That takes time, but on shore power, time is not an issue. Any decent shore powered multi-stage charger will get the battery back to 100% it it's connected long enough.


You'll shorten the battery life more by draining below 50% than you will by having a shore power charger in the garage that doesn't do the "precise" charge profile recommended by the manufacturer.

 

[TerryG]

properly schooled

DiploStrat and dwh: I am grateful for the schooling on this issue. So it sounds like it's the profile that matters and not the "AGM specific" thing. I was planning to get the Optima recommended recharger, so that feedback is reassuring.

So why is draining the battery >50% so bad for it? I'm not electrically sophisticated in the world of batteries and just don't get it. I just thought you could drain that sucker to 0 and recharge it back up...

 

[mhiscox]

I just thought you could drain that sucker to 0 and recharge it back up...

Well, you can, and whereas a flooded battery could be useless after two or three deep discharges, an AGM battery, recharged properly, can be recharged hundreds of times. But the longevity of your batteries will inarguably be lessened the deeper you discharge the batteries before recharging.

This Depth-of-Discharge issue pretty much boils down to how soon you want to buy new batteries. Some notes I had laying around about the Lifeline batteries I have in my Jeep's house battery banks says they should be good for roughly 1,000 charge/recharge cycles with a DOD to the generally accepted 50%. Change that to a 70% DOD, and they'd last 650 cycles. Discharge them 95% and you only get 400 cycles. So the short of it is that constantly doing deep discharges cuts the battery life in half. But you can deep discharge quality AGM batteries without doing them in; it just costs you money for quicker replacement.

I want to stress again that this is not applicable to flooded cells. The rule of thumb for flooded cells is avoid any DOD beyond 30% and, as I said, never deep discharge them, as that'll kill them quick. Kind of explains why lots of people will pay the extra money for AGMs.

 

[dwh]

Well, you can, and whereas a flooded battery could be useless after two or three deep discharges, an AGM battery, recharged properly, can be recharged hundreds of times.

Well...sorry Mike, but no, I think you may be confusing some things.

A thin plate *cranking battery* (whether AGM, flooded or Gel) can be ruined after only a few deep discharges. A thick plate *deep cycle* battery (whether AGM, flooded or Gel) can handle many deep discharges.

Odysseys are special animals which have thin plates but are rated not only for cranking, but also for deep cycle use. [EDIT: Now that I think about it, aren't Lifelines the same?]

But the longevity of your batteries will inarguably be lessened the deeper you discharge the batteries before recharging.

This Depth-of-Discharge issue pretty much boils down to how soon you want to buy new batteries. Some notes I had laying around about the Lifeline batteries I have in my Jeep's house battery banks says they should be good for roughly 1,000 charge/recharge cycles with a DOD to the generally accepted 50%. Change that to a 70% DOD, and they'd last 650 cycles. Discharge them 95% and you only get 400 cycles. So the short of it is that constantly doing deep discharges cuts the battery life in half. But you can deep discharge quality AGM batteries without doing them in; it just costs you money for quicker replacement.

This bit here is totally correct.

Deep cycle battery lifespans are rated in number of cycles, and the lower you drain the battery, the less cycles you'll get out of it.

Here's a life cycle chart from Lifeline, for their AGM batteries:

Here's the same chart, for a Trojan T105 deep cycle flooded:

As you can see, at a regular discharge of 50%, you'll get around 1000 cycles out it.

(Note that being regularly drained to 50% or below, the flooded actually does a little better than the AGM and will live for more cycles. In fact, the flooded can be regularly drained to 60% depth of discharge and still get the same 1000 cycles as the AGM would get being drained to 50%. Draining 100% will get you 350 cycles out of the AGM, but over 500 out of the flooded.)


The "1000 cycles" thing is the reason why everyone prays at the 50% altar.

Kind of explains why lots of people will pay the extra money for AGMs.

Well...it would...if it were true.

 

[dwh]

DiploStrat and dwh: I am grateful for the schooling on this issue. So it sounds like it's the profile that matters and not the "AGM specific" thing. I was planning to get the Optima recommended recharger, so that feedback is reassuring.

That'll work. Last time I looked the biggest Optima branded charger was 12 amps. Optimas can actually handle a lot more charging amps than that. Technically, I think they say "no limit as long as you don't overheat it".

But, what the hell, you can safely use that 12a charger on any lead-acid battery except maybe little wheelchair batteries. But most of them are AGM these days, so even those could probably handle 12a without any problems.

 

[TerryG]

I feel schooled, enlightened, edified, and educated. Thanks to all!!
I thankfully stumbled into the right decisions on my dual battery set up by following the lead of others! Thanks again!!

Also very interesting graphs on the AGM vs flooded batteries.

It's nice to know that I could be out almost every night for 1 1/2 years, draining my battery with an electrical blanket and every other known electrical contraption before I would have to buy a new one. I would love to be out 500 days and nights in the wilds!

 

[mhiscox]

Well...sorry Mike, but no, I think you may be confusing some things. A thin plate *cranking battery* (whether AGM, flooded or Gel) can be ruined after only a few deep discharges. A thick plate *deep cycle* battery (whether AGM, flooded or Gel) can handle many deep discharges.

Yeah, don't know what caused the brain fade there, since I certainly know better; I even came real close to install a Rolls-Surette 6V bank into our first Sprinter. Just got the typical flooded starting battery in my head, I guess. I would have been better to have pointed out the popularity of AGMs for their much faster recharging, much reduced maintenance requirements and their mounting flexibility. Thanks for straightening this out.

 

[dwh]

\It's nice to know that I could be out almost every night for 1 1/2 years, draining my battery with an electrical blanket and every other known electrical contraption before I would have to buy a new one.

Well, there is another issue.

As the batteries age and get cycled, their capacity goes down. So while a battery might be a 100 amp*hour battery when new, if you drain it repeatedly to 100% it's going to lose capacity fairly fast.

A year of doing that and what started as a 100ah battery might only have 50ah capacity. Or less.

Trust me on that - I know because that's exactly how I do it and I have to replace my deep cycle aux battery ever 1.5 - 2 years.

 

[dwh]

Yeah, don't know what caused the brain fade there, since I certainly know better;

I just figured you'd been smoking some of that surfer's whacky weed with J. Suave.

 

[DaveInDenver]

Each type of lead acid battery (AGM, Gel, Open) wants slightly different voltages and different times at each of these stages.

Flooded and AGM battery chargers are often interchangeable but do definitely get a gel-specific charger if that is what you are charging. They do need to be controlled differently to prevent damage. The electrolyte is slightly different in gel batteries and heat needs to be controlled tightly to prevent runaway. They will get very hot and start to bulge when this happens and you'll get a warning in the form a very strong sulfur smell before they go ballistic. If it says universal then it's probably not going to work well for all 3 types and if you're lucky it's safe for gel at the expense of being less then ideal for AGM and/or flooded.

For example:

 

[TerryG]

...Trust me on that - I know because that's exactly how I do it and I have to replace my deep cycle aux battery ever 1.5 - 2 years.

It's nice to know what to expect with real life heavy use, which is my plan.

 

[OregonLC]

How do the Battery Tender chargers rate? I'm running one of these dual channel chargers to two DHP Marine batts.

http://www.batterytender.com/Chargers/2-Bank-International-Charger-12V-1-25A-Each-Bank-USA-Western-Hemisphere.html