Forum Discussion

d-mac1's avatar
d-mac1
Explorer
Oct 17, 2014

12V Battery - Connect a dual purpose with a deep cycle?

One of my 12V dual purpose batteries has a bad cell and the other is fine. I've read on here that the dual purpose aren't preferred cuz we don't need the CCA for a genny so I'd like to replace the bad one with a pure deep cycle battery, but I don't know if there is a downside to having 2 slightly different batteries hooked up in parallel?

I've currently got two of these Deka DP27 (dual purpose) batteries:

http://www.easternmarine.com/deka-12v-marine-master-dp27-dual-purpose-battery

Walmart has the following Everstart Grp 27 deep cycle batteries which per the Q&A has a 109 amp hour rating:

http://www.walmart.com/ip/EverStart-27DC-6-Marine-Battery/16795212#Specifications

I can't find the amp hour rating of the Deka's but it says 150 min at 25 amps.

What do you think? Can I hook a regular deep cycle with the remaining dual purpose?

Thanks!
  • TNRIVERSIDE's avatar
    TNRIVERSIDE
    Explorer
    Oct 17, 2014
    If you do a search on this site you will find lots of good information on the 6 versus 12 volt issue. I just changed to two 6 volt GC batteries.I hope it pays off in longevity.
  • Me_Again's avatar
    Me_Again
    Explorer III
    Oct 17, 2014
    d-mac1 wrote:


    Please tell me more about this change. I'd heard it before but never understood. What is the advantage? Will they start my genny?

    My battery compartment has two 'containers' one above the other in which sit the D27 batteries. Aren't the 6V batteries smaller?


    Golf Cart batteries are about the same width and length as your current batteries. They are however taller by a 1" to 1.5" which might be a problem for you.

    Golf Cart batteries have heavier duty plates and last much longer if taken care of correctly.

    Chris
  • jim1632's avatar
    jim1632
    Explorer
    Oct 17, 2014
    The two battery types are constructed differently for specific purposes.

    A general purpose (starting) battery provides short power bursts to engage the engine. It can be quickly destroyed if subject to deep drawdown/recharge cycles.

    The deep discharge is specifically intended for frequent deep discharge/recharge cycles. It will last much longer in the RV environment where purpose is to get as much 12v for as long as possible and then recharge.

    You want both RV batteries to be deep discharge type, either 12v in parallel or 6v in series. Sorry I don't know why 6v is superior, and its near my bedtime.
  • time2roll's avatar
    time2roll
    Nomad
    Oct 17, 2014
    Generally it is best to get matching batteries if spending money.
    Yes they will work fine together. Expect the new battery to age out along with the old. So if the older battery has 3 years left then expect only 3 years from the new battery.

    If you camp off-grid I also recommend 100 watts of solar.
  • d-mac1's avatar
    d-mac1
    Explorer
    Oct 17, 2014
    Ductape wrote:
    Bad idea. Batteries in parallel should be similar age and condition. When the older battery has a cell go dead it will drag down and kill the newer battery if you're not lucky.

    If your compartment will accomodate best thing would be 2 6V GC batteries and go series.


    Please tell me more about this change. I'd heard it before but never understood. What is the advantage? Will they start my genny?

    My battery compartment has two 'containers' one above the other in which sit the D27 batteries. Aren't the 6V batteries smaller?
  • Ductape's avatar
    Ductape
    Explorer
    Oct 17, 2014
    Bad idea. Batteries in parallel should be similar age and condition. When the older battery has a cell go dead it will drag down and kill the newer battery if you're not lucky.

    If your compartment will accomodate best thing would be 2 6V GC batteries and go series.
  • n7bsn's avatar
    n7bsn
    Explorer
    Oct 17, 2014
    Generally it's best to replace both batteries, as the "old" battery will tend to drag the "new' battery down.

    Generally most of us use true deep cycle, not dual purpose. Dual are really for things like boats, where they also have to start the boat engine. Most people find a regular deep cycle starts the on-board (if any) generator.

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