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Old 28-04-2016, 04:29   #1
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2 AGM 31s to the battery switch -best way?

Hi folks. Just realized I should have posted this here!

I've got 2 new AGM 31 batteries (105 ah rate), and have a handful of suggestions from battery dealers to users as to how to run them to the switch.

One says run one to #1, one to #2, and switch to ALL when charging.
One says run them in parallel and hook to either #1 or #2.
Another says to hook the 2 in parallel and buy another 31 to run to the other post.

Our tri has a single Honda 15 outboard, and we have a Honda 2K generator for trips (like the 4 week honeymoon coming!). We're currently on the dock with shore power, but may move to a mooring and add solar for next year.

Any first hand experience?
Thanks!
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Old 28-04-2016, 05:32   #2
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Re: 2 AGM 31s to the battery switch -best way?

To me it would depend on how big your charging system is. But generally I like one battery bank. If you didn't have the generator I would put the 2- 31s as one bank and a separate smaller start battery. So if I ran down the house bank the 2-31s you can still start. But its your choice.
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Old 28-04-2016, 06:28   #3
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Re: 2 AGM 31s to the battery switch -best way?

Well, the Honda 15 puts out 12 amps, but I doubt that'll do much for keeping the batteries up on trips, hence the Honda 2k.
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Old 28-04-2016, 10:45   #4
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Re: 2 AGM 31s to the battery switch -best way?

AGMs can take a faster charge than flooded batteries. Depending on the charger used it may be faster to charge both at the same time over individualy.
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Old 28-04-2016, 11:03   #5
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Re: 2 AGM 31s to the battery switch -best way?

Even with an outboard for minimal charging, it might be helpful for you to understand these:

Basic Battery Wiring Diagrams This is a very good basic primer for boat system wiring: Basic Battery Wiring Diagrams

This is another very good basic primer for boat system wiring: The 1-2-B Switch by Maine Sail (brings together a lot of what this subject is all about)
1/BOTH/2/OFF Switches Thoughts & Musings | SailboatOwners.com Forums

What are ACRs, Combiners & Echo Chargers? (by Maine Sail)
Battery Switch Question ? | SailboatOwners.com Forums
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Old 29-04-2016, 09:51   #6
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Re: 2 AGM 31s to the battery switch -best way?

it depends on your amp/hr usage in a day. on a 105 ah battery a 60 ah day will bring it down to 50% charge. the out board would have to be run at least 1/3 throttle for 5 or more hr's a day to bring it back up to full. If batteries were in parallel it'd come down too 70 or 80% With a honda 2000 you could run an AC to DC 30 amp charger, cutting your charging time to 2 to 3 hrs. trying to charge both 105 from 70% or less will overload your outboard charger. alternators or magneto charger outputs should be at least 1/3 of the amp/hr rating of the battery bank. the outboard is designed to charge a cranking batt. from no lower than 80% doing more is OK once in a while but not regularly.

that said, I'd run parallel and add a starting bat on a two bank batt. switch. when you go on the hook try to get at least 250 to 300 watts of solar. wind and solar is the best combination tho.

with a hundred watt wind and 205 watt solar south of the 26th parallel I get 120 amp/hrs a day ( i could try to conserve more ;-) but hey? ). Refrigeration/freezer, lighting (LED), inverter - for computer/ entertainment and running/charging other DCV electronics. I don't like buying fuel/gas, so I keep it to a minimum. my 4D batteries stay right around 12.7 to 12.9 and I only have to add water about once every 7 to 8 months...about a pint each batt. on house bank. only once in two years on the engine batt. the smaller the charge/disgharge ratio the long the batt. life.
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