Basic Dual Battery Setup to run Fridge/Freezer questions (sorry in advance if these are dumb)

[Buddha.]

It's not the deep discharge it's that vehicle charging systems are designed for flooded lead acid and usually charge at too low of a voltage.

I feel a bit mislead by the battery sellers then because they list AGM's that work for my truck. Am I wrong?

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[Buddha.]

Is there some specific reason you need an AGM battery? For this type of application the extra cost isn't worth it.

For what application are AGM's worth it?

 

[DiploStrat]

AGM is simply a method of battery construction. By putting the acid in a mat it cannot spill and the battery can be mounted on its side. Also, since it is sealed, it will not gas except under extreme circumstances - perfect for fighter planes. See: https://lifelinebatteries.com/ But, AGM construction can be used to make a starter battery or a deep cycle battery. Lifeline will happily sell you an AGM starter battery or an AGM deep cycle.

AGM batteries tend to be more vibration resistant, can be mounted on their sides, and do not gas, making them "maintenance free" as you do not need to top them up and they tend to corrode their terminals less. They also cost more, and, should you be able to do it, will not recover if they are over charged. (You can't add water.)

For what its worth, GM's Delco batteries are often lead calcium batteries. These batteries offer a lot of bang in a small space, but generally want really frisky charging voltages. These higher voltages (up to 15v at low temperatures) found on Chevrolets and GMC's end up being great for AGM camper battery banks as they help to compensate for voltage loss in the circuit. Some Toyotas and Mercedes Benz, on the other hand, top off at 13.9v, the default voltage for many alternators on the market. (e.g. Bosch). This will do well for your starter battery, but will leave your camper battery undercharged. Hence the development of B2B, which typically boost the voltage and the addition of diodes into the sensing circuit, to boost the voltage.

 

[luthj]

For what application are AGM's worth it?

Applications where long calendar life under light usage is desired. Or high vibration resistance is needed. I have an AGM as a starer battery, it has performed well, and not needing to add water is advantageous. For very cold weather, some AGMs (high plate count pure lead types) have very low internal resistance, and will provide superior cranking amps. In some installations minor acid venting causes corrosion issues, so AGM is needed.

For deep cycling applications, an AGM battery is not ideal due to the general restriction on equalize charging, and higher cost. The major reasons to use an AGM type deep cycling battery are. Extreme vibration, No access for watering, need to mount on the side, etc.

In very high current applications (1C or higher) AGM batteries using pure lead and high plate counts are superior to flooded. They have lower internal resistance, and will have a lower peukert coefficient.

So obviously AGM batteries have their applications, but for a borderline abusive usage case, like running a fridge with poor charging, they will not provide service equal to their price tag.

There are AGM deep cycle batteries that can out perform flooded batteries when charged fully after most cycles. They are expensive. In fact lifeline batteries will perform similarly to flooded batteries of the same class, and can be equalize charged (if done soon enough) to remove sulfation. They are very expensive at around 3$ per AH.

 

[john61ct]

Only time AGM is **needed** is to install on its side, or inaccessible spot for topping up. Or sometime for higher dis/charge rate

Never as good value as FLA per Ah per year, but some are happy to spend more not to bother watering.

Lifeline, Odyssey and Northstar are the good ones

 

[Florida Native]

Only time AGM is **needed** is to install on its side, or inaccessible spot for topping up. Or sometime for higher dis/charge rate

Or if it is installed inside the passenger compartment and not in a sealed box vented to the outside.

-Mike


Sent from my SM-G950U using Tapatalk

 

[shade]

Only time AGM is **needed** is to install on its side, or inaccessible spot for topping up. Or sometime for higher dis/charge rate

Never as good value as FLA per Ah per year, but some are happy to spend more not to bother watering.

Lifeline, Odyssey and Northstar are the good ones

In an automotive environment, how significant is the improvement of AGM construction with regard to vibration? That's the main reason I opted for an AGM starting battery over FLA construction, but if it doesn't really make real difference, I may choose FLA next time.

 

[john61ct]

Assuming equivalent quality of the brand, 100% irrelevant.

Lots of top notch FLA banks last well over a decade in daily use at sea, where shock and vibration are if anything worse than on a land vehicle

 

[john61ct]

Lots of FLA banks are installed inside no special venting.

I an occupant turns out to be sensitive, pretty trivial to take care of the issue as needed.

Ideally just place them in the path of the normal outward bound ventilation, e.g. propane, cooking, fridge heat output

 

[shade]

Assuming equivalent quality of the brand, 100% irrelevant.

Lots of top notch FLA banks last well over a decade in daily use at sea, where shock and vibration are if anything worse than on a land vehicle

Good to know. Since I don't often find the engine bay of my truck upside down, I may go FLA next time. Thanks!

 

[john61ct]

High ambient temps are not conducive to good longevity

 

[shade]

High ambient temps are not conducive to good longevity

That goes for FLA & AGM, right? May as well spend a little less for FLA if it's going to suffer from the effects of heat as much as AGM.

 

[luthj]

Temp degradation is basically constant for all lead types. Now, as the plates corrode and shed material, it can build up at the bottom of the case in flooded, and eventually cause plate shorts. Or the plates themselves can fracture. This is not a significant issue on quality batteries, as they have enough space at the bottom of the case, and use thick enough plates (with separators).

An AGM battery is more resistant to this damage, as the cells have physical support. But there is no reason that a good flooded won't perform the same when designed for it.

For durability the lifeline/northstar AGM batteries with porous Polyethylene separators and dense glass mat are incredibly hard to break. But the conditions that would require then in a vehicle would also wreck the vehicle in short order. Think Baja 1000.

The bottom line is a quality flooded battery will provide equal service in the average application for less cost.

If you need to avoid/reduce watering, there are VRLA (valve regulated Lead Acid) batteries which are flooded. They have a thicker case and usually some catalyst in the lid. This reduces water loss significantly. You would still need to choose one with a fill port, so you can top up every year, as they are not truly "maintenance free".

 

[john61ct]

Quality deep cycling FLA is more robust generally, and being able to top up the electrolyte level is a huge advantage. In general, both lower cost per Ah **and** longer lifespan, so **much** lower amortized cost per year.

Also much less fussy about proper care requirements, can make do with a greater variety of less precise charge sources.

If a sealed battery is overcharged for whatever reason **and** ambients are very high, then the destructive off-gassing or seepage cannot be remedied.

The only sealed batteries I'd reco for deep cycling usage are the top AGM, or GEL type from Sonnenheim or EPM. The latter can be made to last as long as FLA, but are **very** fussy about care parameters, really require user-adjustable profile setpoints and can't be fast-charged.

 

[john61ct]

My reco list for FLA in the North American market is

Rolls/Surette, Trojan, Deka/East Penn, U.S. Battery, Crown and Superior.

The best battery value in the world by far is usually Duracell (actually Deka/East Penn) FLA deep cycle golf cart batteries, 2x6V, around $200 per 200+AH @12V pair from BatteriesPlus or Sam's Club. Deka labeled same batts also sold at Lowes.

Sometimes you can find Trojan T-105 GCs locally within 10-15% of those, would also be tremendous value.