AGM vs. Lead Acid for solar (in 2017)

[devero4]

Looking for some help from the solar gurus... I have been seeing a lot of skewed information regarding which type of battery is recommended and which is not, as far as solar goes. I currently have a 100W Renogy panel with a 20Amp PWM controller. The system is a house battery system that only powers my Engel fridge and charges a cell phone. I keep reading that Marine AGM batteries are not recommended, and to go towards the Deep Cycle Lead Acid route. Any advice would be appreciated, sorry if this has already been discussed.

 

[Joe917]

Marine branded batteries tend to not be deep cycle. You can get both AGM and flooded as deep cycle.
Flooded golf cart batteries are the most cost effective solution, I can recommend Trojan. I would only spend the extra on AGM if I had to install the batteries in the living quarters or in an inaccessible location.

 

[devero4]

The battery will be in between the fridge and back seat, inside the vehicle. It is easily accessible by folding the seat down. I guess what I'm asking is; What battery would better suite my needs and not be prone to over charging: Deep Cycle AGM Marine, or Deep Cycle Sealed Lead Acid?

 

[dwh]

AGM is lead-acid.

AGM is Sealed Lead-Acid (SLA) with fiberglass mats sandwiched between the lead plates to act as a sponge for the acid.

AGM and GEL are always SLA. Flooded (sloshy) Lead-Acid (FLA) can either be sealed (SLA FLA) or not.

FLA, AGM and GEL can all be had with thin lead plates (cranking use), thick lead plates (deep cycle use), or a compromise with medium thickness plates (labeled RV/marine) that can do either job - but not as well.

While charging, water gets split into hydrogen and oxygen. In a SLA, there is a catalyst in the cell caps to recombine them into water. With an open cell vented battery the hydrogen and oxygen (rocket fuel) just vents outside the battery. Water has to be manually added to replace what was lost.


For use inside the cabin of your truck, you certainly want a sealed (SLA) battery to keep the hydrogen in the battery. Whether you go with an AGM SLA, GEL SLA or FLA SLA is up to you.

If you aren't cranking, then you should choose a deep cycle battery. But if you are prepared to accept a bit less performance and lifespan, the RV/marine compromise battery will also get the job done.

 

[dwh]

As to overcharging. You won't overcharge an AGM or FLA by driving. Chronic undercharging due to short drive times is far more common.

You might overcharge a GEL - they generally have a lower voltage limit.


The primary purpose of a solar charge controller is to prevent battery overcharging.

 

[devero4]

Thanks for the great info, dwh. And for setting me straight on battery types. However, my panel is on top of my 4Runner, and is separate from the vehicle's charging system. The float charge on my controller is set to 13.3V, and the fridge only runs on the weekends. (So that's why I was concerned about the overcharging)

 

[john61ct]

First off, you only want true deep cycle, no 12V AGM sold in auto or big box retail meets that standard, their "marine" and "deep cycle" labels are fraudulent.

Next, overcharging is rarely an issue, chronic undercharging is the norm, and drastically shortens bank lifespan

The best value by far is ​Duracell (actually Deka/East Penn) GC-2 from BatteriesPlus or Sam's Club deep cycle golf cart batteries, 2x6V

They will store 200+AH for under $180, and all you need is a cheap hydrometer to accurately monitor State of Charge.

True DC AGM will be much more, and are only worth it IMO if you need to install them sideways or can't get to them with a hydrometer, or need the faster high-amp charge acceptance.

Plus AGM is more susceptible to less than ideal conditions, so the Deka GCs are best for a first bank.

 

[devero4]

A lot of good info here, thanks everyone. I need to stop reading the interwebs, because I always find conflicting information. But is it true that AGM batteries need to be charged a certain way? All I have is a Cheaper PWM controller, so Im hoping that holds up, should I get a AGM battery

 

[jonyjoe101]

You will never overcharge your agm with solar. On my agm I had the absorb/bulk set to 14.4 volts and the float to 14.3 volts (the highest it would go). The 3 years I had it was connected to a solar panel with those voltages. The agms like to be kept at those voltages. To overcharge an agm, you need to charge it with over 15 volts of power, you have to force the battery to take the amps, then it will vent. When I first got into solar I was using a jump pack (17ah agm) as my aux battery connected to a 120 watt solar panel, never got overcharged or damaged in the 3 months I used it.

With solar many times when the battery reaches a certain voltage it will switch to float this will prevent the battery from getting a full charge. The battery has to remain above 14 volts (absorb) for many hours (actually all day long) to get a proper charge. You run out of sunlight before you fully charge it. But if you can keep the float at 14 volts or higher, then you maximize the charge.

If your floating at 14 volts and your battery is consuming about 1 amp of power ,that is good, it means your almost fully charge. There are some highend agm that you need to fully charge them with a high amp charger (50 amp) every once in a while to properly maintain them.

If you going to have the battery indoors, you need an agm sealed battery. I sleep near where my agm is, never had problems with it venting etc. For your 100 watt panel, that cheap pwm is all you need. I was using a 10 amp pwm controller on my 240 watt panel, they are reliable. You just can't adjust the voltage on them. Some people will run out and try to get an mppt controller to get more amps but with a small low voltage (20 volt) panel you wont get an improvement. For mppt to work you need a 30 volt or higher panel.

 

[dwh]

But is it true that AGM batteries need to be charged a certain way?

Not really. A couple do. Odyssey is one.

 

[Ducky's Dad]

I would not drive a vehicle with an FLA mounted in the cab. Don't want the risk of an acid spill in event of an accident or rollover. In cab, it's AGM all the way for me. FLA OK in the bed of the truck.

 

[grizzlyj]

AGM is lead-acid.

AGM is Sealed Lead-Acid (SLA) with fiberglass mats sandwiched between the lead plates to act as a sponge for the acid.

AGM and GEL are always SLA. Flooded (sloshy) Lead-Acid (FLA) can either be sealed (SLA FLA) or not.

FLA, AGM and GEL can all be had with thin lead plates (cranking use), thick lead plates (deep cycle use), or a compromise with medium thickness plates (labeled RV/marine) that can do either job - but not as well.

While charging, water gets split into hydrogen and oxygen. In a SLA, there is a catalyst in the cell caps to recombine them into water. With an open cell vented battery the hydrogen and oxygen (rocket fuel) just vents outside the battery. Water has to be manually added to replace what was lost.


For use inside the cabin of your truck, you certainly want a sealed (SLA) battery to keep the hydrogen in the battery. Whether you go with an AGM SLA, GEL SLA or FLA SLA is up to you.

If you aren't cranking, then you should choose a deep cycle battery. But if you are prepared to accept a bit less performance and lifespan, the RV/marine compromise battery will also get the job done.

:sombrero:

 

[e60ral]

For charging requirements just check for the battery you are looking at. I know the East Penn/Deka 8A and 8G batteries want charge/absorption/equalize of 13.8V to 14.6V, and a float/standby of 13.5V +/- .01V

 

[Step-Hen]

I would not drive a vehicle with an FLA mounted in the cab. Don't want the risk of an acid spill in event of an accident or rollover. In cab, it's AGM all the way for me. FLA OK in the bed of the truck.

I agree. If you have an FLA battery fused and securely mounted in a good battery box which is itself securely mounted (not "it doesn't slide around much" secure, but "it's going nowhere if I roll my vehicle" secure) AND use a high quality charge controller with a charge profile that is suited for the battery, the risks of something going wrong are pretty low...however, if something does go wrong, an FLA will vent hydrogen gas and sulfuric acid much more readily than an AGM. Let me tell you, acid in the eyes and lungs is not a pleasant experience.

 

[Step-Hen]

The primary purpose of a solar charge controller is to prevent battery overcharging.

I agree from the standpoint of safety, since dangerous things can happen when a battery gets overcharged, but I'd say the primary purpose of a charge controller is to make maximal use of available solar energy while ensuring good battery life. It's an important distinction because it's tempting to buy a $20 charge controller on ebay, only to find out after your battery dies prematurely that all the charge controller did was shut off the voltage when it got to a certain level, usually less than the battery manufacturer recommends (if they bother to provide that information.) Most PWM and MPPT charge controllers, which are generally more sophisticated than "eBay specials," have a very limited ability to match their charging parameters precisely to a given make/model of battery.

Having said that, I'll admit that it's surprisingly difficult to get objective information on why optimizing the charging profile is important, so you have to accept anecdotal (albeit grouchily compelling) evidence from the likes of HandyBob, or oversize your batteries and replace them more often. I did recently find some slightly vague information published by Odyssey, however, that shows that you get 2-3X the number of cycles out of their batteries if you charge to 14.7V instead of 14.2V (page 14 of US-ODY-TM-002_1214.pdf- I'd be interested in other opinions on whether I'm interpreting the information correctly.) It's possible that the data apply only to their batteries, but my guess is that any LA battery would show similar results. Assuming that's what Odyssey is really saying, it makes a pretty compelling argument for highly adjustable charge controllers with at least 3-stage charging.