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Battery ratings

rbpru
Explorer II
Explorer II
I know from past experience that a battery’s ratings are not always proportional. I have a class 27 battery rated 20 A at 105 AHrs. That should mean a half load for 210 hrs or double load for 52.5 hrs. but that is not always true.

I am planning a week without shore powder and using the battery electric for just for the water pump and lights at night when needed.

I have yet to measure the phantom loads to on the 12 volt size but the micro-wave and TV are all wire to the 120 volt side, which leaves only the TV pre-amp, the various detectors; and the radio/DVD player on the 12 volt side. I am thinking the vaious 12 volt fuses should effectively kill them.

The question is; drawing at most 10 amp per hour, how many hour would I get out of my battery.

Also, never having tryed this, before what am I missing.
Twenty six foot 2010 Dutchmen Lite pulled with a 2011 EcoBoost F-150 4x4.

Just right for Grandpa, Grandma and the dog.
13 REPLIES 13

ADK_Camper
Explorer
Explorer
The size of your battery and it's chemistry aside, any battery will last longer if you put less demand on it. That said you should try to accurately determine the phantom load on your battery and try to control that. Those phantom loads often put a continuous demand on your battery. In my camper I discovered that the most significant load was the refrigerator. As said your control board needs 12 V to operate. Nothing you can do about that short of turning the refrigerator off, but there may be another significant demand placed by your refrigerator. There may be a heater around the door gasket that is supposed to prevent condensation in humid weather. Some refrigerators have a switch to control this heater. If yours does, turn it off to greatly extend your battery life. If, as in my case, the heater cannot be turned off you can find the wire supplying 12 v to the heater and disconnect it. I actually installed a switch in that line so I can turn the heater on and off. Actually since I installed the switch I have never turned it back on and I have never had a condensation problem.

beemerphile1
Explorer
Explorer
bcarroll wrote:
This seems like a good thread to use to ask questions about batteries...
I was looking at batteries at Walmart and a grp 24 RV/Marine Deep Cycle battery is listing 100ah @ 1a. It also lists 600 CCA.
Then I went to Costco and saw grp 24 RV/Marine Deep Cycle batteries that had 600 CCA but no ah rating.
Then I also see other batteries listed as grp 24 that have a 50ah rating. Is there that much difference on ah ratings for the same grp of batteries?

The more I read up on batteries the less I seem to know about them...
Is there a way to compare different brands of batteries on a level playing field?


A new thread started by you would be the best place to ask. Now that you have revived this old thread some people will respond to the original poster and some will respond to you making things confusing.

In brief, a group 24 battery is typically 80 to 85 ah @ 20hr.
Build a life you don't need a vacation from.

2016 Silverado 3500HD DRW D/A 4x4
2018 Keystone Cougar 26RBS
2006 Weekend Warrior FK1900

Community Alumni
Not applicable
The AH (Amp Hours) are generally the numbers to go by. The battery that didn't have a AH rating should have a RC (Reserve Capacity) rating. The reserve capacity is a similar, but different rating system. Divide the RC minutes by 2.4 to quickly convert it to AH. Disregard the CCA (Cold Cranking Amps). Generally this is unneeded since we aren't starting any engines.

The internal makeup of the battery ultimately determines the AH capacity. This is why you're seeing the variance between batteries in the same group. The surface area of the plates, amount of plates, and acid amounts all help determine the capacity of a battery. These batteries are mostly targeted to the boating industry. Boats need high amps for starting motors, but also a decent capacity for electronics and whatnot. Several thin plates, like car batteries, will give high amps, but a fairly short life. Fewer thick plates, like golf cart batteries, will increase longevity, but can't generate the high amps needed. They're trying to strike a balance between the two.

bcarroll
Explorer
Explorer
This seems like a good thread to use to ask questions about batteries...
I was looking at batteries at Walmart and a grp 24 RV/Marine Deep Cycle battery is listing 100ah @ 1a. It also lists 600 CCA.
Then I went to Costco and saw grp 24 RV/Marine Deep Cycle batteries that had 600 CCA but no ah rating.
Then I also see other batteries listed as grp 24 that have a 50ah rating. Is there that much difference on ah ratings for the same grp of batteries?

The more I read up on batteries the less I seem to know about them...
Is there a way to compare different brands of batteries on a level playing field?

RJCorazza
Explorer
Explorer
proxim2020 wrote:
A 105 Amp Hour @ 20 Hour Rate battery discharging at 10 amps will give you around 8.5 hours of run time. If you're mathematically inclined, have a look at Peukert's law.

I was aware of Peukert's Law, but was suprised to see such a large difference between the 5 and 10 amp discharge rate.
At one time I was really into lead acid battery charging, chemistry, etc... but I have forgotten much of it.
As several have pointed out, the thread went in a more theoretical direction with total battery capacity (100% discharge), when in practical use the battery should not be discharged to more than 50% on a regular basis. So with the original inquiry we are down to about 4 hours of battery use.

Lowsuv
Explorer
Explorer
What I have been doing for a baker's decade :
I use a # 2 AWG x 12 foot jumper cable to tie the 2 Edge AGM's in my duramax to the TT batteries .
That gives me 4 batteries to run from .
My pickup gets driven every 2nd or 3rd day .
When I return I just connect the jumper cable again .
I do not run the truck to charge the TT batteries .
I have no solar or genny .
Each summer we camp 9 days without hookups at our secret lake .
I could tell you where it is but ....

westend
Explorer
Explorer
OK you've got the math but don't plan on getting that kind of use from your battery. I don't know, off hand what the cut out levels are on the circuit boards and alarms inside you rig but they will be reaching a threshold value before the battery is down to 10.5V. Also, if you choose to drain the battery with a larger load down to 10.5, in a few cycles, you'll be looking for a new battery.

If you plan to go a week, I'd suggest to look at carrying two batteries.
'03 F-250 4x4 CC
'71 Starcraft Wanderstar -- The Cowboy/Hilton

rbpru
Explorer II
Explorer II
RJ

Thanks for the info. If I understand correctly the 20 hrs is the industry standard for measuring discharge time from full charge to 10.5 volts. (The useful voltage range).

Therefore, whatever that amount of current may be times the 20 hrs is the standard amp-hour rating for the battery.

In my case 5 amps times the 20 hour is 100 amp-hours, close enough to the 105 AH.

Thanks again
Twenty six foot 2010 Dutchmen Lite pulled with a 2011 EcoBoost F-150 4x4.

Just right for Grandpa, Grandma and the dog.

Community Alumni
Not applicable
A 105 Amp Hour @ 20 Hour Rate battery discharging at 10 amps will give you around 8.5 hours of run time. If you're mathematically inclined, have a look at Peukert's law.

RJCorazza
Explorer
Explorer
I am not sure I understand your battery rating statement, but to clear things up, your battery has a 105ah capacity when discharged to 10.5v over 20 hours. So at a discharge current of about 5 amps the battery is effectively at zero capacity in 20 hours.
So you can expect (slightly) less than 105ah at a 10a discharge rate, for all practical purposes 10 hours.

2oldman
Explorer II
Explorer II
rbpru wrote:
battery rated 20 A at 105 AHrs...; drawing at most 10 amp per hour, how many hour would I get out of my battery.
Being conservative and realistic:

105ah/10a = 10.5hr. However, you can effectively only use 1/2 of that, so, about 5 hours. You can't drain it to 0 volts -battery ah ratings are extremely unrealistic.

And it's not 'amps per hour', it's just amps. 10 amps drawn continually for 1 hour is..ta da.. 10ah.
"If I'm wearing long pants, I'm too far north" - 2oldman

bid_time
Nomad II
Nomad II
In my experience, using the water pump normally (no showers), frig, and lights sparingly, we could last a week.

mbopp
Explorer
Explorer
Even on propane your 'fridge needs 12V to operate, probably 300-500ma when the gas solenoid is on.
You shouldn't draw down a battery past 50% or 12.00V, so your effective capacity is less than you think.
2017 Grand Design Imagine 2650RK
2019 F250 XLT Supercab
Just DW & me......