4D vs 8D battery

Discussion in 'Marine Electrical / Electronics' started by Raider Ronnie, Nov 29, 2019.

  1. Raider Ronnie

    Raider Ronnie Captain

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    Pro/cons
    I’m told 4D is just as many CCA, lighter (weight) and last longer.
     
  2. djmarchand

    djmarchand Captain

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    Maybe the specs on some 4Ds equal or exceed some 8Ds, but in general the bigger battery provides more CCAs.

    David
     
  3. Raider Ronnie

    Raider Ronnie Captain

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    8D. 1450 CCA
    245 amperage hrs

    4D 1420 CCA
    198 amperage hrs

    The starting battery in the Flowers (8D) is junk even though previous owner said it was only 1 year old. (Not sure I believe that or not)
    House battery is also an 8D
     
  4. cb34

    cb34 Captain

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    Series 31 plenty for start, 2 6 volts for house. Why sail with or have to lift a 8d?
     
    cb34,
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  5. Raider Ronnie

    Raider Ronnie Captain

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    Not my doing.
    It’s how the boat was when I bought it.
    Will say the 8D house battery May be necessary with all the things in the boat (bow thruster, ac/heat, big anchor winch, how water heater, lots of electronics ect...)
    Pretty sure the starting battery is just for starting.
    The boat also has 2 alternators.
    1 for starting battery, other for house
    Separate battery switches and a bypass battery switch to connect the 2
     
  6. RCLS2016

    RCLS2016 Senior Member

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    I don't want to speak out of turn but, 4D & 8D batteries are typically for starting and or high draw very short duration loads based on the CCA (Cold Cranking Amp) rating. Depending on engine size or the cranking amps needed.... Deep cycle batteries have a RCA (Reserve Capacity) rating, and can be drawn down upwards of 75% without damaging the plates. Making them much better for house loads. ie: stereo, pumps, radar, chart plotter, etc... Also the design of the plates in a deep cycle battery are more friendly to your electronics because they act like a filter. I have a Deere 6068 and would trade my 8D for a 4D if it was time for a new battery for starting if I had the opportunity. A bow thruster or windlass is a huge load but intermittent, and I would definitely keep that on the 4 or 8D Battery.
     
    Last edited: Nov 29, 2019
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  7. Pedlyr

    Pedlyr Senior Member

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    I would think the Group 31 would be fine for starting. But if it were me I would want the 8D for the house.
     
  8. TCL

    TCL Senior Member

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    I have 2 Group 31 for my starting batteries, fairy easy to move to their resting place outside of the Starboard engine. Previous boat had 4D's way too heavy.
     
    TCL,
  9. Dslpwr

    Dslpwr Senior Member

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    I’m going with 4 group 31 in series parrallel in 24 volts.Just to save weight in handling in the engine room. All my over the road trucks use 4 group 31’s. My boat is just a lobster boat plus if I went with a bow thruste I would go with a hydraulic one.
     
  10. Gurryman

    Gurryman Captain

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    I ordered my first class 8 truck with 4 delco group 31 625 CCA batteries. They lasted 14 years before needing replacement
     
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  11. ARC

    ARC Senior Member

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    I replaced 2- 8d’s . It was a mistake I should have done 4 group31’s . 1 had to add a auto fill setup because I could not reach the outboard cells.
     
    ARC,
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  12. Wharf Rat

    Wharf Rat Captain

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    4Ds and 8Ds are NOT the same, as farlasting longer, that's BS; it's all about how you take care of them not to mention it can be apples to oranges depending on the type, and that goes for flooded lead acid OR AGM. Also, there are batteries designed for cranking, some for 'dual purpose', and some for deep cycle.

    That said, the battery should have a sticker with a letter/number indicating its age, and even if that's gone, the manufacturer will stamp into the plastic the actual date it was built. So from what I gather this is for starting. How old is the house bank's 8D, and more importantly, are they getting charged via the same charger/alternator.

    Also, all batteries are not created equal, even if they have the same specs as CCA or AH Capacity. WHat exact batteries do you have now and how are they getting charged?
     
  13. xbskt

    xbskt Captain

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    I went from a pair of 8D to group 31 when I refreshed the Crowley. Big mistake for my installation.
    I only have two batteries. No house bank. No space. The 31s start the motor fine. They are lighter but for me that is a less important factor in hindsight.
    Now when I start or restart all my electronics shut down and need to restart.
    Big PITA.
    Never was aproblem with the bigger batteries and when they are toast I will go back to 8Ds.
     
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  14. BillD

    BillD Captain

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    same setup in my 25 TJ with the 370 Cummins, pr of 31s
     
  15. BillD

    BillD Captain

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    the new to me 27 H&H has four 6 volt batteries. Two cabled together to get 12 volts.

    I've found the best setup for my needs is a pr. of 31 starting batteries and a deep cycle 27 size for the WHOLE house. I don't run much...but never have to "reset" everything on an engine start.
     

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  16. Diesel Jerry

    Diesel Jerry Captain

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    I had always been an 8D fan, but after changing so many over the years I am changing my ways. Depending on the situation I would go with 6Volts in series, or group 24, 27, or 31s in parallel. Unless you can put that 8D somewhere were you can get it in and out easily.
     
  17. Raider Ronnie

    Raider Ronnie Captain

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    My main objective is not have to replace a battery every 1-2 years which has been my experience even with the BHM. (Group 31s)
    Maybe the place I’m buying them from sell crap batteries
    The batteries in the Flowers, according to previous owner were new last year. @ $500 + for an 8D I certainly don’t want to have to replace every year.
     
  18. BillD

    BillD Captain

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    T-105 | Trojan Battery Company

    Motive AGM | Trojan Battery Company

    The 27 H&H came with four new 6 volt Trojans. Cabled together in series to get 12 volts per bank.
    I've always run West Marine 31 Marine AGMs.. had good luck with them.

    I'm not an electrical engineer. How BIG is my 12 volt battery using two T-105 6 volts?

    31 ? 4D ? 27?
     
  19. Wharf Rat

    Wharf Rat Captain

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    With FOUR of those batteries wired for 12V, each battery being 6V Ea at a 225 AH, you'd have a total of 500 Ah capacity. Huge amount for a house bank. Typically a single 8D is around 240Ah. Some might have a lower CCA and higher Ah, but what you have is like the equivalent of two 8Ds in parallel.

    The way it works with series/parallel is if you connect in series, the voltage doubles but Ah stays the same. Connect in parallel, voltage stays the same but Ah capacity increases. Yours is a combination of both, so you have a heavy duty 12V bank with four 6V T105s.

    For anyone who is looking to go the Group 31 route on a house bank, super important you don't get a cranking battery. It's important to A. Have a high Ah capacity. B. Make sure you're going with a very good battery manufacturer. West Marine uses East Penn for their AGMs, AKA Deka. These are calcium based lead, and I would consider to be the best value in AGMs. Lifeline makes an excellent group 31, the GPL-31XT. Odyssey is also worth mentioning with their TPPL (Pure Lead) 31M battery.

    If you want the absolute best, look at the Firefly Oasis, which is a Carbon Foam AGM. There's nothing out there that can compete with that battery when it comes to true deep cycling, and it's important to understand how crucial it is for a battery to recover from a deep state of discharge. A dead battery isn't 0.0V, it's 11.8. That is a ZERO PERCENT state of charge. Batteries have a hard time living a long time when just discharged to 50%, which is around 12.3VDC. I don't want to hijack this thread going off on a state of charge tangent, but take a look at the link below for that Oasis battery, which if you scroll about halfway through has a couple of links to some independent tests by Compass Marine for Practical Sailor, and Nigel Calder who is like a God in the marine electrical world tested the shit out of them as well. There's a good video there too.
    Firefly Oasis Battery - Carbon Foam AGM
     
    Last edited: Dec 2, 2019
  20. hardcore1

    hardcore1 Captain

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    something is wrong if you are replacing batteries every 1-2 years. run those 8ds til they are no good. interstate makes a 4d deep cycle that is reasonably priced and will start your engine no problem when its time to replace.
     
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