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2 Dual Purpose Batteries vs 1 starting/1 deep cycle

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View Poll Results: 24' center console - 2x dual purpose vs 1 cycle/1 starting
2 dual purpose
7
33.33%
1 deep cycle + 1 starting
8
38.10%
2 starting
1
4.76%
2 deep cycle
5
23.81%
Voters: 21. You may not vote on this poll

2 Dual Purpose Batteries vs 1 starting/1 deep cycle

Old 10-06-2020, 07:32 AM
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Question 2 Dual Purpose Batteries vs 1 starting/1 deep cycle

Are dual purpose batteries any good or jack of all trades, master of none? I have a 2 battery setup in my 24' center console. Right now they are both starting/cranking batteries but I am looking to swap them out. I had planned to get one deep cycle and one starting battery. Dual purpose batteries seem interesting and if I had 1 battery, I think it would be a no brainer but with 2 is it better to go with 2 dual purpose or one deep/one starting?

For additional discussion, AGM vs acid?

Last edited by merlin2375; 10-06-2020 at 07:40 AM.
Old 10-06-2020, 09:49 AM
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I use deep cycle AGM batteries for both cranking and house. The catch is they have to be able to provide sufficient MCA/CCA which means they're big. I'm fine with that.
Old 10-06-2020, 09:55 AM
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Hi Drako - my current batteries are both group size 24, I was going to replace them with 24s again. Are you saying that you had to go with a larger battery to get what you needed in terms of CCA?
Old 10-06-2020, 10:01 AM
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Yes. Look up what your outboard specifies for CCA and then check what your battery can provide -- it's not just the group size, compare the specs for MCA/CCA. Deep cycle batteries typically have less CCA than similar cranking batteries.
Old 10-06-2020, 10:11 AM
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Originally Posted by merlin2375 View Post
Hi Drako - my current batteries are both group size 24, I was going to replace them with 24s again. Are you saying that you had to go with a larger battery to get what you needed in terms of CCA?
what are your house loads?

what are you starting?
Old 10-06-2020, 10:32 AM
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House loads - Chartplotter, radar, stereo, VHF, courtesy lights, livewell
Starting - 1 x Yamaha 250xca
Old 10-06-2020, 11:50 AM
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How were the group 24s treating you?

Do you plan on adding more house loads in the near future?

How are the batteries being charged?

without knowing anymore specifics of your vessel, and if she was mine, I would:

grp 27 start and grp 27 deep cycle.

and AGM is a type of lead acid battery. You have three types of lead acid: Flooded, AGM, Gel.

they all have their pros and cons.
Old 10-06-2020, 01:16 PM
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Originally Posted by Onebadlarry View Post

without knowing anymore specifics of your vessel, and if she was mine, I would:

grp 27 start and grp 27 deep cycle.

and AGM is a type of lead acid battery. You have three types of lead acid: Flooded, AGM, Gel.


Old 10-06-2020, 01:18 PM
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oops

Last edited by coores14; 10-06-2020 at 01:22 PM. Reason: double post
Old 10-06-2020, 01:21 PM
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oops

Last edited by coores14; 10-06-2020 at 01:22 PM. Reason: triple post! dang you THT!
Old 10-07-2020, 07:15 AM
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Thanks for the replies. Good points.

1) I will have to change out the batt trays to go from 24 to 27 group size, not a huge problem but would have to do so.
2) When one has two batteries, is there anything that says the two batteries have to be exactly the same?
3) Seems like most AGM batts are dual purpose not starting vs deep cycle? Am I missing something?
Old 10-07-2020, 07:24 AM
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I would use 2 Group 27 dual purpose. That's what I have on my 20' w/Yam 150. I've always been told the batteries should be the same or you'll throw off the charging system. Not sure how much fact was behind it, but it came from a supposed "battery guy". The reason why a lot of the AGM are Dual is, for the most part, you want to have a "back up" for starting and the standard Deep Cycle won't do it. In my double setup, my normal routine is to run #1 on the Saturday and #2 on Sunday. If I sit with the engine off for more than an hour and something running, then I'll put my switch in "both" if she tries to drag a little at startup, but rarely do I need to. This routine has worked pretty well for me and keeps both batteries in-use and sufficiently charged. Of course, I'm a stickler for charging at home the night before too.
Old 10-07-2020, 07:43 AM
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I have 1 Group 24 starting battery and 1 Group 27 deep cycle battery.
Old 10-07-2020, 10:21 AM
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Originally Posted by merlin2375 View Post
Thanks for the replies. Good points.

1) I will have to change out the batt trays to go from 24 to 27 group size, not a huge problem but would have to do so.
2) When one has two batteries, is there anything that says the two batteries have to be exactly the same?
3) Seems like most AGM batts are dual purpose not starting vs deep cycle? Am I missing something?
if you plan on using an ACR/Combiner/VSR or a charger when on the hard, then yes, same type of battery.

two of the same exact AGM 27s (labeled deep cycle or dual purpose)will be A ok to use on your boat. Just make sure they meet minimum CCA.

Last edited by Onebadlarry; 10-07-2020 at 10:28 AM.
Old 10-07-2020, 10:25 AM
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Originally Posted by merlin2375 View Post
Thanks for the replies. Good points.

1) I will have to change out the batt trays to go from 24 to 27 group size, not a huge problem but would have to do so.
2) When one has two batteries, is there anything that says the two batteries have to be exactly the same?
3) Seems like most AGM batts are dual purpose not starting vs deep cycle? Am I missing something?
No need for them to be exactly the same. Personally I would want the same chemistry (all AGM or all flooded) simply because charge profiles are largely the same within a given type. This insures that the voltage/charge regulation system can operate at its best.
Old 10-07-2020, 03:31 PM
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Run 2 group 24 deep cycle batteries. Interstate/Costco wet cell batteries lasted me 9 years. They were still cranking well when it seemed prudent to buy new ones.
They start my DF300ap without issue.

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