House battery capacity

[woodscrew]

Does anyone know how to calculate amp hour ratings for batteries? I have two Deka 908D batteries tied together for 24 volts as a house bank. Each one is CCA 1400 and RC 430. How does that relate to amp hours for the whole bank?

 

[High Wire]

Does anyone know how to calculate amp hour ratings for batteries? I have two Deka 908D batteries tied together for 24 volts as a house bank. Each one is CCA 1400 and RC 430. How does that relate to amp hours for the whole bank?

IF they are connected in series, then the voltages ADD (12V plus 12V = 24V) but the AmpHour capacity stays the same.
IF they are connected in parallel, then the voltage stays 12V but the AmpHour capacities add together.

 

[tiltrider1]

It’s really hard to tell you how many amp hours you can get out of starting batteries. If all these batteries do is house work then you have the wrong batteries. If they are for starting engines then you have the correct batteries. If you are trying to do both jobs from the same set of batteries then you will need to compromise.

 

[NWSeadog]

All the above is true. In a compromise application you can take the Reserve Capacity and divide it by 2.4 to get Amp Hours. And remember if you pull more then 40 to 50% of the Amp Hours out of the battery you will significantly shorten their life.

You can call East Penn who is the manufacturer. They are usually quite helpful.

 

[Russell Clifton]

If the amp hours are listed on the battery than they are starting batteries and not made for deep cycle applications.

 

[DavidM]

Those batteries are obviously not true deep cycle if there is no amp hour capacity listed. And there is only an approximate relationship between CCA and Ahs although a 1400 CCA battery is pretty big, maybe an 8D.

David

 

[rgano]

If the amp hours are listed on the battery than they are starting batteries and not made for deep cycle applications.

Did you miss a "not" in there somewhere?

 

[Russell Clifton]

Darn-it anyway.. Yes I did. Must be that covid vaccine I got today.

 

[ranger58sb]

Deka specs:

https://www.eastpennmanufacturing.com/wp-content/uploads/0007-DEKA-SLI-Spec-Sheet.pdf

The 908D doesn't have an amp-hour rating listed; looks like a starting battery, not dual-purpose, certainly not deep-cycle.

FWIW, a typical dual-purpose 8D generally has 220-245 Ah... but starting batteries wouldn't be that high...

-Chris

 

[TBill36]

Fully charge you batteries - should be 12.82v for 12v batteries. Put a load on them and measure the amp drain. Time it for a 4 hrs. This will give you the amt of amp hrs that you have removed from the batteries. Then measure the voltage and compare to the state of charge chart. Example - you pull 10 amps for 4 hrs, gives you 40 amp-hrs. If you measure 12.2 after the 4 hrs then you have 50% state of charge. Result is 80 amp-hr batteries.

 

[rgano]

Darn-it anyway.. Yes I did. Must be that covid vaccine I got today.

Yeah, my first one was no biggie, but I understand the second one might be a bit tougher. I will use that excuse on Feb 18th!

 

[woodscrew]

Thanks for all the replies. A lot of good info to digest. When I bought the boat in 2012 I had the yard replace all the batteries. Both the house and start banks are 24 volt. The Deka series 27 engine start batteries are still working fine. The Deka 8D house batteries lasted until last May. I keep them all clean and topped off with distilled water. Honestly I never even thought about what they were. 8 years of service was good enough for me, so I replaced them with the same thing. They were lightly used both in depth of discharge and number of cycles for the first five years. I have new refrigeration that draws more than the previous unit. On the hook (at CayoCosta) for six days I had to run the genset more often than I am used to. Started me thinking about doing some math on loads and amp hours etc. Turns out that my own laziness was the apparent source of the trouble. My old Vitrifrigo fridge needed defrosting every two to three weeks or it wouldn’t hold temp. The new Isotherm DR 160fridge freezer combo seemed more forgiving of longer periods between defrosts. So much so I let it go way too long and it was cycling on a lot as a result of the excessive ICE buildup.Defrosted it yesterday and got 11 hours before I hit 50% discharge. Major improvement. When I wear out these batteries I will replace with deep cycle batteries. Thanks again. Any favorites for deep cycles? Lead acid vs gel?