Batteries for 21ft CC

SkaterRace said:

I have a 21ft CC with a 2019 Merc 225XL OB and during my pre-spring prep I noticed 1 battery will not hold a charge and the other is weak. They are 5 years old so it's likely time to replace. The current ones are Nationwide part 31T-GS, which has CCA of 1000 and a RC of 185.

I have a few options and was hoping to get some opinions from more knowledgeable people (I've always used the Motomaster batteries before this boat)

Motomaster Nautilus group 31 deep cycle battery 890 MCA and 190 RC

LiTime 12V 100Ah Max discharge current 1/5s 500A/300A

Power Queen 12.8V 100Ah LiFePO4 Max discharge current /5s 280A

Out of the above options which would be my best bet ignoring price?

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dingbat said:

What is min CCA for your motor?
The last two batteries are storage, not starting batteries

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cyclops222 said:

Trolling motor thrust and voltage ?
how many watts is your sound system ? Hours at what power level during each cruise? Hours while anchor ?
Does your engine start every time in less than 2 or 3 seconds? Hot or cold motor ?
Does the engine try to recharge the batteries ?
I like to keep the same battery chemistry for all batteries.

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cyclops222 said:

You can safely use any battery that is at least meeting those 2 ampere specifications. Your motomaster size 31 is ideal for your boat. Buy 2 and cruise.
Do check the tiny label on EACH battery. It states when each battery was made. NOTHING older than 3 months normally. No ? Go to some other place. Have the batteries LOAD TESTED. Watch the test meter. Any jerky readings ? Reject it. Request another new battery. A lower cost Lead Acid battery is all you need. Enjoy.

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SkaterRace said:

According to the manual, it is "800 minimum marine cranking amps (MCA) with a minimum reserve capacity of 135 RC25 rating"
I think that means the motomaster is fine? Though a lot of people online say 1000 CCA is the lowest to go with.

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dingbat said:

A lot of people apparently don’t know the difference between MCA and CCA battery ratings

The difference between MCA and CCA is the temperature which the test is conducted. The MCA test is conducted at 32F while the CCA rating is conducted at 0F.

Use the following formula to compare batteries of different ratings:

1,000 MCA x 0.77 = 770 CCA
1,000 CCA x 1.3 = 1,300 MCA

Your current battery is roughly 168% of recommendation but is also an automotive starting battery. Switching to a more robust “dual purpose” battery would be my suggestion.

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SkaterRace said:

In terms of a more robust dual purpose battery, what do you mean?

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dingbat said:

It's all about battery construction and the batteries ability to withstand the abuse of (multiple) deep discharges.

Automotive Lead-acid batteries are designed for short bursts of high energy. i.e. starting the engine and short term powering of accessories. They’re not built to be discharged below 10.5 volts under load or 11.8 volts at rest w/o being compromised. Think parasitic drain, stuck bilge pump, ignition left on, excess radio usage, etc.

On the other hand, a dual purpose (hybrid) or deep cycle batteries are designed to withstand multiple, deep discharges and live to see another day.

Note the disparity between the expected Cycle Life of Starting and Deep cycle batteries below

Chemistry	Starter (SLI) Flooded, sealed	Deep-cycle Flooded, sealed	AGM VRLA*
Type	Many thin plates increase the surface for high current delivery,	Fewer thick plates give high capacity and durability,	Sulfuric acid is absorbed by a fine fiberglass mat.
Discharge rate	High momentary current​	Continuous moderate current Moderate to high current​	Continuous moderate current Moderate to high current​
Cycle life (full DoD)	12-15​	150–200, longer if not discharged lower than 60% SoC​	150–200, longer if not discharged lower than 60% SoC

I actually use RV batteries that give me 620 CCA (recommended) of starting current and 108 Amp Hours of storage, each.

Have both batteries on a switch with a ACR. If push comes to shove, I can combine both batteries to provide 200% of recommended CCA.

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SkaterRace said:

I ended up with the MotoMaster Nautilus.

I read on the MCA vs CCA before hand though barely understood much past the basics.

In terms of a more robust dual purpose battery, what do you mean?

Yeah the old ones were automotive since I guess that dealer must get a good deal or something since it is in all of their boats.

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