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Old 05-17-2019, 06:52 AM   #1
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Batteries - Comparing apples to oranges

I currently have two 12 volt marine deep cycle batteries. These are a group 24 battery. I need a little more reserve capacity, but don't have room to add more batteries, so I'm going to replace the existing G24s with GC2's, they'll fit in the compartment.

The group 24 are rated in CCA, the GC2 are rated in amps @ 20min.

Since there really isn't a good way to compare these numbers. I'm looking at using the weight as a reasonable comparison.

i.e. My two G24s weigh 86 lbs. I'll replace them with two GC2s that weigh 136 lbs. If I look just at weight, this should give me approximately 30% increase in capacity..

QUESTION - I know this isn't exact and there are numerous other considerations, BUT, is this a somewhat reasonable assumption??
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Old 05-17-2019, 07:16 AM   #2
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From a physics point of view it is a reasonable assumption.

On a more practical level the fact that the two 24 group batteries you have are rated in cold cranking amps indicates they are engine start batteries, not TT house batteries. However, Marine batteries often are dual use, house and small engine start. It is possible the amp hour rating is on the label, just not easily visible. It may say ah or AH or something similar

Assuming the new batteries are for use as TT house batteries, switching to deep cycle (deep draw) batteries would provide a much better experience. The golf cart batteries you propose would be a good choice. I like AGM batteries because the have many advantages for TT use. Unfortunately they cost as much as twice as much.
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Old 05-17-2019, 07:35 AM   #3
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There is a way to convert RC to AHs if you can find that spec on the gp 24 batteries.

My MH came with 2 new GP24 batteries. They were rated at 55 AH.

The 2 of them didn't equal 1/2 the capacity of of a pair of GC2, 6 volt batteries.

You will be happy with the pair of GC2s.
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Old 05-17-2019, 07:58 AM   #4
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Size is one thing, chemical make up and design is another. If you have the brand and make of your current G24 you can do the math quick vs a replacement.

If you want more capacity why not get 1 (100AH Lifepo4) battery? 29lbs vs 150lbs.

Something to think about if you are boondocking. They will also charge twice as fast so less gen time.

https://battlebornbatteries.com/comp...teries-series/
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Old 05-17-2019, 08:58 AM   #5
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Quote:
Originally Posted by Waiter21 View Post
QUESTION - I know this isn't exact and there are numerous other considerations, BUT, is this a somewhat reasonable assumption??
For flooded lead acid batteries, this is a VERY reasonable way to compare !

Marine "deep cycle" batteries are a COMPROMISE ! They are NOT true deep cycle batteries. The only TRUE 12V deep cycle batteries are either golf cart batteries (GC12 like Trojan T-1275 or T-1275 AGM) or are "solar energy" batteries (like Trojan SSIG line). Both of these are much more expensive than a marine 12V battery or a pair of GC2 batteries.
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Old 05-17-2019, 11:04 AM   #6
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For flooded lead acid batteries, this is a VERY reasonable way to compare !

Marine "deep cycle" batteries are a COMPROMISE ! They are NOT true deep cycle batteries. The only TRUE 12V deep cycle batteries are either golf cart batteries (GC12 like Trojan T-1275 or T-1275 AGM) or are "solar energy" batteries (like Trojan SSIG line). Both of these are much more expensive than a marine 12V battery or a pair of GC2 batteries.
I installed 3 of these Northstar AGMs. Northstar Battery NSB-AGM 27M
Some will say they are not "true" deep cycle batts but I disagree. They can go down to 80% discharge. They replaced my failed POS Exide AGMs that almost blew us up.
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Old 05-17-2019, 05:32 PM   #7
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My RV was equipped with two (2) NAPA 12v Group 24 Marine/RV batteries (62 AH each, according to NAPA). Replaced with two (2) Duracell 6v GC2 AGM batteries (190 AH each, according to Duracell). AGM is virtually maintenance free... downside is about 50% weight increase over the 12v batteries.

Used original battery hold-down, needed longer hold-down bolts (12") and spacers (between hold-down and battery) to clear vent caps on 6v batteries.
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Old 05-17-2019, 11:39 PM   #8
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Quote:
Originally Posted by twinboat View Post
There is a way to convert RC to AHs if you can find that spec on the gp 24 batteries.
Quote:
Originally Posted by kdauto View Post
I installed 3 of these Northstar AGMs. Northstar Battery NSB-AGM 27M
Some will say they are not "true" deep cycle batts but I disagree. They can go down to 80% discharge. They replaced my failed POS Exide AGMs that almost blew us up.
IMHO, any battery that does NOT have an advertised "reserve capacity" is not a TRUE deep discharge lead acid battery.
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Old 05-18-2019, 09:57 AM   #9
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Quote:
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IMHO, any battery that does NOT have an advertised "reserve capacity" is not a TRUE deep discharge lead acid battery.
What's your point ?

The battery mentioned lists a RC spec.
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Old 05-18-2019, 11:12 AM   #10
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Quote:
Originally Posted by kdauto View Post
I installed 3 of these Northstar AGMs. Northstar Battery NSB-AGM 27M
Some will say they are not "true" deep cycle batts but I disagree. They can go down to 80% discharge. They replaced my failed POS Exide AGMs that almost blew us up.
The choice is yours but I would not consider $370.00 for 91 AH to be a good investment for an AGM battery. I would think Lifelines (or something similar) would be a much better choice for that price and longer cycle life.
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Old 05-18-2019, 11:24 PM   #11
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The choice is yours but I would not consider $370.00 for 91 AH to be a good investment for an AGM battery. I would think Lifelines (or something similar) would be a much better choice for that price and longer cycle life.
We got them for 400 CDN each, about 300 USD. I found nothing affordable in lipo at 1500 plus each and sizing was another issue. I just searched for that brand and see NO difference in what we have. Ours are deep cycle and decent reserve capacity. I am a professional mechanic and garage owner so I am quite familiar with batteries.
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Old 05-19-2019, 11:01 AM   #12
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Quote:
Originally Posted by kdauto View Post
We got them for 400 CDN each, about 300 USD. I found nothing affordable in lipo at 1500 plus each and sizing was another issue. I just searched for that brand and see NO difference in what we have. Ours are deep cycle and decent reserve capacity. I am a professional mechanic and garage owner so I am quite familiar with batteries.
The link you provided for the original poster to consider as a replacement for what he has (2 group 24 marine batteries with a combined AH capacity of about 150) would be a poor choice since he stated he had room for 2 GC2 6v batteries.

Your suggestion would give him 2 12v AGM batteries with a total of 182 AH capacity at a cost of (your price) $600.00 US (although the current price appears to be $740.00).

Two of Lifelines GPL-4CT AGMís at a present cost of $620.00 US would give him 220 AH capacity in a by far superior battery. By my math that is a 21% increase in capacity at a (most likely) cost savings from what you recommended.

What you chose and have with your available space may have been the best choice for you BUT is a poor choice for the original poster in his situation.
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Old 05-19-2019, 11:56 AM   #13
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Quote:
Originally Posted by 757driver View Post
The link you provided for the original poster to consider as a replacement for what he has (2 group 24 marine batteries with a combined AH capacity of about 150) would be a poor choice since he stated he had room for 2 GC2 6v batteries.

Your suggestion would give him 2 12v AGM batteries with a total of 182 AH capacity at a cost of (your price) $600.00 US (although the current price appears to be $740.00).

Two of Lifelines GPL-4CT AGMís at a present cost of $620.00 US would give him 220 AH capacity in a by far superior battery. By my math that is a 21% increase in capacity at a (most likely) cost savings from what you recommended.

What you chose and have with your available space may have been the best choice for you BUT is a poor choice for the original poster in his situation.
It appeared as though you were responding to me and stating that my choice of battery was poor and not true deep cycle.

I simply explained what we had and specs,which really are pretty good. We could debate the minutiae for days but in the end there are minor differences and at that, only on paper. I can not find the brand you mentioned anywhere locally. Northstars I linked are branded under different names.
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Old 05-19-2019, 12:14 PM   #14
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Cool

Quote:
Originally Posted by theoldwizard View Post
IMHO, any battery that does NOT have an advertised "reserve capacity" is not a TRUE deep discharge lead acid battery.
Automotive engine start batteries are designed for short very high discharge to start an engine. These will not do well for TT, RV, or marine house battery duty. You can measure or calculate an amp hour capacity for them. You can not change their physics to work well as house batteries.

Marine applications are similar to TT, and RV house use. There are large marine engines to start, but they need the same automotive engine start batteries as RV engines. Smaller engines can be started from large deep cycle "Marine" batteries just like RV's that use large inverters to run house hold appliances. These marine house batteries are true deep cycle batteries.

Gulf Cart batteries are also true deep cycle batteries. They are typically used in large banks and are usually optimized for cost-benefit of frequent fast charge followed by deep discharge.

Stationary solar batteries (also made by Trojan) are high capacity, slow charge and discharge designs.

For part time TT use where the TT is used on a few weekends each year and an annual longer trip, marine AGM batteries are ideal (Yes, Trojan makes CG AGM batteries too). Yes you must pay significantly more for them, but they will typically last much longer than flooded cell batteries.

Flooded cell batteries need frequent maintenance and don't take kindly to neglect or accidental flat out discharge.

AGM's last twice as long in storage. They never need acid level monitoring. They tolerate a few flat out discharge cycle with minimal damage. They can be installed inside in living spaces.

There is much more to learn if you are so inclined.
Battery University

https://batteryuniversity.com/
How does the Lead Acid Battery Work? https://batteryuniversity.com/learn/article/lead_based_batteries
Summary Table of Lead-based Batteries https://batteryuniversity.com/learn/article/bu_214_summary_table_of_lead_based_batteries
Charging lead acid batteries https://batteryuniversity.com/learn/article/charging_the_lead_acid_battery
GEL https://batteryuniversity.com/learn/article/bu_201b_gel_lead_acid_battery
AGM https://batteryuniversity.com/learn/article/absorbent_glass_mat_agm
Charging with Solar, Turbine https://batteryuniversity.com/learn/article/charging_with_solar_and_turbine
How to Charge and When to Charge? https://batteryuniversity.com/learn/article/how_to_charge_when_to_charge_table
How to Store Batteries https://batteryuniversity.com/learn/article/how_to_store_batteries
Summary of Doís and Doníts https://batteryuniversity.com/learn/article/do_and_dont_battery_table
What is a Deep Cycle Battery?
https://marinehowto.com/what-is-a-deep-cycle-battery/
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