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Using Black & Decker BM3B 6V and 12V Battery Charger / Maintainer's DC accessory plug

Hello Everyone,

Anyone have thoughts on using this charger through the boat's DC accessory port to keep both batteries charged over the winter?  The Black & Decker BM3B.

Paul Bolden


United States Coast Guard Aux, VFC, FSO-VE


  • cjjjdeck
    cjjjdeck Member, Moderator Posts: 1,872 ✭✭✭✭
    Interesting product, especially with the cigarette lighter adapter.  Decent reviews.  It looks like it's really just a maintainer, so your battery needs to be in a decent state of charge prior to using it (which is what I assume your using it for anyway).  I've read that it will not charge batteries that are at 2 or less volts.

    Both batteries?  Not sure.
    2012 SD237 I/O Mercruiser 5.0L MPI ECT/ Bravo 3
    2012 Load Rite Elite Tandem axle trailer

  • FlyingV5
    FlyingV5 Member Posts: 154 ✭✭✭

    Some advice from a retired mechanic: I would use separate chargers for each battery and keep the batteries electrically isolated from one another during charging. If one battery fails, it can "pull down" the good battery if they are connected. Your automatic charger can be rotated between the two batteries by plugging it in to the accessory socket and selecting the desired battery with the battery selector switch. Or just use two of those little "cube" float chargers to avoid over cooking the batteries and keep the selector switch in "off" position.

  • pbolden
    pbolden Member Posts: 45 ✭✭
    Thanks guys, I decide to get two of these chargers.  One for each battery.
    United States Coast Guard Aux, VFC, FSO-VE