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Thread: Installing extra battery

  1. #1

    Default Installing extra battery

    Help. I want to install a second battery for my boat. I have a 150HP outboard, and I won't need a bunch of deep cycle juice to power refrigerators or any appliances on board. I basically just want to have a back up battery in case my primary battery goes belly up for some reason.

    Do I want to get another starting battery, a dual use battery, or a deep cycle battery? Thanks in advance!!!

  2. #2

    Default Cheapest

    Based on what you state that your needs are, get a starting battery. Be sure to get a marine battery because they'll take a pounding better than an automotive battery. Costco has good prices on marine batteries.

  3. #3
    Join Date
    Apr 2006


    You also do not have to go to the trouble and expense of adding a second battery and the switch.
    Most of the drains we see on batteries is what I heard referred to as "parasitic drain". This means the electronics on our boats require just a small amount of juice even when they are turned off. Even with the battery switch turned off bilge pumps cand still operate and run if there switch is stuck open.
    I would suggest you simply carry an extra charged starting battery and store it out of sight. If it is fully charged when you place it on your boat it will hold a full charge for at least 2 months. Just do not have it connected to anything. Or if you are paranoid about losing juice just top it off with the charger once a month. If you ever need it, it would be easy to swap it out.

  4. #4
    Moderator Paul H's Avatar
    Join Date
    Apr 2006


    Personally I'd go the slight extra effort and expense of wiring in the extra battery with a switch, and an isolating relay so both batteries can be charged at the same time. When it rains it poors, and if you battery pukes in pitching seas, you really don't want to be moving a battery around the deck.

  5. #5

    Default Just completed a backup system

    Check out the Hellroaring battery isolator/combiner. It's probably among the best systems out there and very easy to install. If nothing else read their writeup and it will be informative. Also West Marine has a very good writeup in their catolog.


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