HMD19 Battery Cable Extension

Power Boats only. Please include the boat type in your question.
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Re: HMD19 Battery Cable Extension

Post by blueflood »

Hey guys thank you for the replies.

Doug N...this is great. I don't suppose you can forward photos of your set-up to "" or we can discuss ovee phone ? I would like to talk if possible.

Yes it is a Group 21 AGM. I can get all the parts required from a few narine shops around here and AWG pre terminated cables of different lengths as well.

I will go measure the boat this evening and also the Merc cables to see what is required.


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Re: HMD19 Battery Cable Extension

Post by fallguy1000 »

Just to be clear, ABYC has made no accomodation and all battery lockers require venting. An AGM battery, while technically sealed can still outgas hydrogen sulfide?, but if it does, it does not breathe back and so agms get waffled if overcharged and heated up.

It did happen to me because I thought I could draw 12v off a 24v bank. What happens is the bank is constantly overcharging the 'good' one. And I waffled an AGM. So, the experience is real to the textbook reasons.

Any battery locker should be relatively easy to vent outside the living space.
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Re: HMD19 Battery Cable Extension

Post by Cowbro »

Doug N wrote: Thu Aug 11, 2022 2:38 pm Hello Marc
I have done just what you're wanting to do. I have junction posts in the starboard aft locker with both the positive and negative cables from the outboard landed there and then continuing to the helm bulkhead with 4 gauge cables. You can add another couple of feet to that as the cables go from a off/on/combine switch to the start battery. My 9.9 spins over very well on the starter but I haven't checked voltage drop. The start battery is an old agm (8 yr at least) that was rated at 100ah when new. I have a couple of crimpers so the wiring went fairly well. What type of battery do you have? If you put a flooded lead acid inside the cabin it is recommended to vent it outside which causes a bunch more work. I went with some salvaged agm's from old solar powered sites and have they have worked out well.

I did the same thing with my HMD. Battery is up front, these boats need all the weight up front that they can get. I have a terminal block under the gunnel with heavy Guage wiring to the battery to extend the outboard cables. Our little 9.9 kickers don't draw much juice. I wouldn't worry too much. I think the factory cables on my EFI Suzy are only 8 gauge.

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