Cruisers Forum
 


Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 17-01-2025, 13:57   #1
Registered User

Join Date: Apr 2024
Posts: 5
Replace 12 AGM House deep cycle battery and add 2nd 12 volt AGM battery cabling

Hi I want to replace my stand alone House 12 Volt AGM 27 and would like to add a second House battery to increase the off shore power cycle for my refrigerator.
I am in Ontario, Canada. My Boat is a 2001 Doral 360Se and has dual 7.4 Mercs which have separate 12 volt starting batteries.
Questions:
1. Where in Ontario can I get a good/best Deep Cycle 12 volt AGM 27 size battery?
2. Should I connect the 2 batteries in series or parallel for max deep cycle off shore power?
3. Is it OK new second 12 volt deep cycle battery is about 2.5 to 3 feet away from current House battery?
4. I have a generator as well.
5. When connecting a power gauge to monitor the battery power, what is the proper method to connect it to the 2 House batteries?

Wade Kranz
wadekranz is offline   Reply With Quote
Old 17-01-2025, 16:02   #2
Registered User
 
Reefmagnet's Avatar

Join Date: May 2008
Location: puɐןsuǝǝnb 'ʎɐʞɔɐɯ
Boat: Currawong 30
Posts: 4,897
Re: Replace 12 AGM House deep cycle battery and add 2nd 12 volt AGM battery cabling

1. Can't help
2. Parallel.
3. That's fine, but preferably connect the positive house lead to one battery and the negative house lead to the other battery. This will help keep the battery voltages balanced with each other. Make sure to use leads of a suitable size to reduce the voltage drop for the parallel connection.
4. Get a suitable charger for AGM batteries if you haven't already got one for the generator. Don't use it's "DC charger outputs" if it has them as these aren't intended for this purpose.
5. You treat the batteries as a single unit in parallel, and use a "coulomb counter" style of monitoring gauge. These use a shunt connected between the negative battery terminal and the house supply. Victron is one brand that makes this type of gauge.
Reefmagnet is offline   Reply With Quote
Old 17-01-2025, 18:54   #3
Moderator
 
Adelie's Avatar

Join Date: Feb 2010
Location: La Ciudad de la Misión Didacus de Alcalá en Alta California, Virreinato de Nueva España
Boat: Cal 20
Posts: 21,601
Re: Replace 12 AGM House deep cycle battery and add 2nd 12 volt AGM battery cabling

Quote:
Originally Posted by wadekranz View Post
Hi I want to replace my stand alone House 12 Volt AGM 27 and would like to add a second House battery to increase the off shore power cycle for my refrigerator.
I am in Ontario, Canada. My Boat is a 2001 Doral 360Se and has dual 7.4 Mercs which have separate 12 volt starting batteries.
Questions:
1. Where in Ontario can I get a good/best Deep Cycle 12 volt AGM 27 size battery?
2. Should I connect the 2 batteries in series or parallel for max deep cycle off shore power?
3. Is it OK new second 12 volt deep cycle battery is about 2.5 to 3 feet away from current House battery?
4. I have a generator as well.
5. When connecting a power gauge to monitor the battery power, what is the proper method to connect it to the 2 House batteries?

Wade Kranz
1. Why do you want AGMs? If you discharge them very deeply (>25% DoD, ie 75% full) they need to be recharged at a high C-rate. AGMs need to be bulk recharged at 0.2C minimum. 0.3C is a better target. 0.3C for a 200Ahr bank (2 group 27 batteries in parallel) is 60amps. Can you get 60amps from one of your alternators? If you want low maintenance get GEL batteries. If you have good access and don't mind watering your batteries every 2-3mo then get a good Flooded Lead Acid (FLA) like Trojan which will be significantly cheaper than the other 2 types.
2. Parallel. If you wire in series you need to have 24v accessories which there are not a lot of compared to 12v.
3. Shouldn't be a problem as long as you tap the positive and negative feeds from different batteries. (see sketch) Actually it's a good idea to tap from opposite ends even if they are right next to each other.
4. If you use this to recharge and you have a big charger (75Amps) you could stay with the AGMs.
5. Follow the instructions with the gauge.
Attached Thumbnails
Click image for larger version

Name:	Parallel Battery Bank Opposite ends tap..png
Views:	10
Size:	6.4 KB
ID:	297836  
__________________
Num Me Vexo?
For all of your celestial navigation questions: https://navlist.net/
A house is but a boat so poorly built and so firmly run aground no one would think to try and refloat it.
Adelie is offline   Reply With Quote
Old 18-01-2025, 03:47   #4
Registered User

Join Date: Apr 2024
Location: Seychelles is vessel base
Boat: Leopard 51 PowerCat
Posts: 300
Re: Replace 12 AGM House deep cycle battery and add 2nd 12 volt AGM battery cabling

For “power gauge”, imho best is a shunt with Ah meter. Going by voltage to estimate battery state is not very useful. You’d add the shunt inline to the negative side of the bank, meaning shunt sits between your negative cable and the negative pole.
Johan Leopard51 is offline   Reply With Quote
Old 18-01-2025, 14:47   #5
Registered User
 
NorthCoastJoe's Avatar

Join Date: Mar 2016
Location: North of San Francisco, Bodega Bay
Boat: 44' Custom Aluminum Cutter, & Pearson 30
Posts: 927
Re: Replace 12 AGM House deep cycle battery and add 2nd 12 volt AGM battery cabling

Your batteries should be the same age. Why not get a Lithium battery and go with a small DC/DC charger off your start battery. That would be simpler and more cost effective.

https://www.amazon.com/Victron-Orion...s%2C175&sr=8-7

https://www.litime.com/products/liti...ifepo4-battery
NorthCoastJoe is offline   Reply With Quote
Reply

Tags
agm, battery

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Can I run an AGM battery in paralel with a deep cycle Lead Acid? And if not.... momo034 Electrical: Batteries, Generators & Solar 5 15-01-2022 15:08
What cabling do I need to add another Raymarine i70s on port side? Cool Hand Luke Marine Electronics 2 02-12-2019 04:03
12 volt deep cycle OR 2 6 volt LTH batteries info please XANADU.WS.32 Electrical: Batteries, Generators & Solar 21 18-11-2018 06:51
Replace A Starting Battery With A Deep Cycle Sailuke Electrical: Batteries, Generators & Solar 3 13-04-2016 11:33
Best mains battery charger for 12 volt Deep Cycle wet lead acid batteries Triumphant Electrical: Batteries, Generators & Solar 19 13-07-2015 00:25

Advertise Here


All times are GMT -7. The time now is 05:22.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2025, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2025, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.