Place(s) to buy AGM battery for best pricing.

I hope this chart disproves what Amazon Customer stated.
amp hr capacity, 20 hr. Room temp the battery is discharged down to 10.5v or so at a constant current and timed. Repeat for different current. Repeat Curve fit data and use formula to determine 20 hr capacity.

look at this chart, the first is G24 battery, note at bottom the 20 hr capacity is 69 ah.
now look at the 6A discharge and note it takes 10.7 hrs with a capacity of 64 ah. So the 10.7 hr capacity is 64 ah which is less than 20 hr capacity of 69 ah. 69/20 = 3.45A constant discharge for 20 hrs.



check sams/costco for duracell AGM G31

 

Battery capacity varies by the discharge rate. A battery discharged at constant 5 amps will output more amps than if discharged at constant 10 amps. So you would expect a battery that outputs 100 AH at 20 hour rate to only output about 93 amps at the 10 hour rate. By stating "100 AH @ 10 hour rate" They're making a veiled claim that their battery is superior to one that outputs 100 AH @ 20 hour rate. The question is, do you believe it? Is it achievable in the real world?

The amazon customer is probably confusing amp hours with reserve capacity. Which is rated by discharge rate and results in minutes of run time. RC is normally stated at 25 amp discharge rate, RC @ 25 amps = 140 minutes. But I've seen battery advertisements stating RC at 10 or even 5 amp rates, which definitely skews the result.

 

Several years ago, Sams Club had the best deal on AGM G-31 batteries. There 105 AH AGM battery right mow is $179. It use to ne in somewhere around OCT, NOV of each year they would have a sale on the batteries. It's the same battery that west marine sells for about 275

 

in these test 10.5v under whatever load is considered DEAD or 0% SoC.


Reserve Capacity (RC)
1. Allow fully charged battery to stand at room temperature for 4 to 96 hours.
2. Discharge battery at 25A at 80 +/- 5 degrees F (27 +/-3 degrees C).
3. Determine discharge time in minutes to 10.5V for a nominal 12V battery.
4. Correction for final discharge temperature: Mc=Mr[1-0.009(Tfinal-27)]
Mc = minutes corrected to 27 degrees C (80 degrees F)
Mr = minutes actually run
Tfinal = temperature of electrolyte above plates in a intermediate plate in degrees C
0.009 = temperature correction factor
AH capacity (AH)
1. Follow procedure for RC test except run at designated discharge rate (either n hour discharge rate or at specified amps). For example 20 hour capacity would be tested at nominal 20 hour discharge rate, i.e., 20 hour capacity in AH divided by 20 hours (105AH/ 20 hours = 5.25 amps. AH capacity may also be determined at a specified amp discharge rate, say 1, 5, or 10 amps, etc. The rating system is specified by the battery manufacturer. JCI marine batteries are normally rated at the 1A discharge rate.
2. Upon determining the discharge time to 10.5V in miniutes. Convert to AH with the formula: AH = Mr X A / 60, where
Mr = minutes actually run
A = discharge rate in amps
3. AH capacity available in the field is temperature and rate dependent and could deviate significantly from the rated value. Increased AH's are available at warmer temperatures and lower discharge rates.

 

Yes 10.5 all. The AH and RC standard is Just that a standard that is to be used if rating a battery for AH's. It defines how how the voltage should be dropped, the temperature etc.... for the test.

 

I would third checking out the Sam's club batteries. They are Duracell brand, which is East Penn (DEKA). Price as stated above and about 4-5 times a year, you can purchase them for an additional $20 off. I have the G31 FLA on my pop up and it works great. (Duracell) We can go for 10 days on this battery, but we don't draw a lot other than recharging stuff and lights.

 

Crown battery and Trojan are considered upper quality batteries by most. The marketing manager for Crown said that the Lead Acid battery is a superior design to the AMG. The only reason to buy an AMG was your willing to sacrifice everything for a non off gassing battery.

There are two different types of plates; rolled and stamped. I am pretty sure it is stamped that is the less favorable form of making and the type Costco and Sam's use. Trojan and Crown use rolled.

Six months ago I did the math. The Trojan costs the same on a per year basis BUT it costs more up front because they last about 8 years.

I'm going Trojan next time as Crowns are hard to get.

 

My understanding the "dual purpose" is also known as a marine battery. A true deep cycle is a golf cart battery.

https://handybobsolar.wordpress.com/2019-lithium-batteries-truth/

 

Better make sure you have an appropriate charger for Trojans which require an unusual bulk charging voltage of 14.8 volts vs the more commonly recommended bulk charging voltage of 14.4 volts.

FWIW, so-called Duracell flooded batteries, AGMs, GELs are in fact manufactured by East Penn, the largest battery manufacturer in the US. Here in Canada they're sold at 60+ RV Care dealerships under the Traveler's Choice name - but they're the identical batteries. Bought a Group 31 myself.

 

where's your G31DC documentation on charging?

 

GreyFox, I have respected your knowledge of electrical and since you didn't criticize it must mean I am learning.<GG>

Somewhere buried in my saved paperwork there is a charger that has a smart module. You can dial in the voltages for bulk, absorption, and float. There has been some criticism that 14.8 may be a tad high.

A couple months ago we quit using the converter to charge the house battery and switch over to solar. The converter never got up to 14.4 when checked. The solar got up to 14.4 every sunny day. The battery now has higher CCA as measured by a local auto store. Also it doesn't seem to discharge as quickly sitting in the basement. Unfortunately the specific gravities were not permanently recorded as I plan to check them today to see if solar has helped them. 1 and 6 used to be weak.

 

But you have twice the amp capacity. Longer periods between charging. I have a CPAP that has to be fed and investigating ways not to babysit a charger. It's taking away from my hiking time.

Trojan is supposed to have 12 VDC true deep cycle. The next time we go to town the plan is to stop by the largest Trojan distributor in the state and talk to them.

 

Here's a Trojan battery spec sheet for their SCS200, picked at random ...

http://www.trojanbattery.com/pdf/datasheets/SCS200_Trojan_Data_Sheets.pdf

Bulk charging voltage is spec'd at 14.82 volts along with the reminder that temperature compensation is critical. The typical trailer converter isn't capable of either, even many stand alone chargers aren't either, particularly temp compensation. The decision as to which battery to buy shouldn't be based on just the battery but also the charging system one intends to use to maintain that battery. I'd speculate that the vast majority of RV owners don't pay attention to either, just buy what is available and cheap, and blindly destroy that battery prematurely by ignoring these important issues. Check out other Trojan batteries here and you'll see specifications for each battery they offer ...

https://www.trojanbattery.com/

... buy a different brand and you'll have a different set of specifications. Here's East Penn's battery offerings ...

http://www.eastpenncanada.com/

For anyone interested here's a East Penn technical manual that explores the vagaries of their own brand of AGM and GEL batteries.

http://www.eastpenn-deka.com/assets/base/0139.pdf

 

I'll speculate that there are those who aren't fighting a CPAP who take the attitude that if they could improve battery life by 40% that's "only $40.00 US" on a Walmart special.