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Hey fella's - question for the battery guru's out there for a 150 Optimax ProXS:

Battery 1 - 27M6 specs CCA 840 CA 1050 RC 182

Battery 2 - AGM 8A31DTM specs CCA 800 CA 1000 RC 210

Aside from one being a AGM, what are the performance differences? Is the AGM a superior battery, even with the slightly lower CA and CCA?

I'm upgrading from the 27M6 to a AGM - thoughts????

Thanks

Google explains the difference

Hey - Battery expert here!

The answer really depends on what you want it for. If you are looking for a battery that will simply start your boat then the top one (regular type) with the higher cranking amps is your best bet in terms of peformance/cost tradeoff.

But if you are looking for something that is going to run accessories then the AGM is far superior.

The RC is "Reserve Capacity" given in Minutes, which confuses the heck out of people but is actually pretty easy to understand. It is "number of minutes battery can power a 25 amp load". If you are running your aerator, fish finder, radio and lights... then you are probably in the range of 12 amps.

So battery 1 at RC of 182 minutes would power 25 amps for 3 hours, or 12 amps for about 6 hours (when new)
battery 2, at RC of 210 minutes will give you 3.5 hours or at 12 amps will give you 7 hours. Not a bad increase.

But where AGM really shines is in cycle life and vibration abuse. If you have a pretty big motor and the battery is mounted near it, then AGM will last longer than anything else. If you also tend to run the battery down quite often, then AGM is also going to pay for itself in the long run.

AGM is also slightly better in hot temperatures.

Most military vehicles that have critical batteries in them will be running AGM today (although hopefully soon they will be using Lithium).

Hope the above helped, feel free to ask any other battery questions.

Steve.

Scarkner explained it pretty good.

With the Optimax needing such a high CCA and to ensure it is there when I would need it, I would more than likely go with the AGM because the RC is a little bit higher. I imagine you will be running graphs and such off of this battery so the bigger the RC, the better provided the MCA or CCA meet the requirements of the motor you are trying to start.

Post on iBoats, measured cranking amps of a 2008 Optimax 250 XS Pro at 170 amps.

This is inline with my expectations for a V6, even running fairly high compression because the Optimax is using a gear-reduction starter. A 1000 amp starter cable is bigger than your thumb, the lines to your motor are likely the diameter of your pinkie finger (still pretty big, but not the size that we see running to a 2000 hp diesel).

Scarkner,

I only bring up battery size for motor because the Optimax requires a battery with 800MCA or 1000CCA to start it.

Thanks for the responses, fella's - appreciate that!!

So, let me shed a little more detail on the situation at hand. Motor is 2015 150 ProXS. Original battery is/was the 27M6 - recently, with HDS10, HDS5, Elite 7 and livewell pumps running, my motor failed too start twice (once last season and I dismissed it as a fluke incident).

Thinking it was a battery issue and not wanting to encounter the problem again, I replaced it last week with the AGM 8A31DTM. As a precaution, I enabled the low voltage feature on the HDS units. This past weekend were the first two outings with the fully charged battery. After a few hrs with all the electronics running, I go turn the engine on and the low voltage warning (11 V is the default setting for low warning) appeared on the screen - no issue with the engine starting, though. This happened each time during the day when I started the engine to move locations - again, no issues starting engine.

What are your thoughts? Is the low voltage warning just erring on the side of caution (should I disable the setting on the HDS)? This has me stumped ...................

Thanks

That depends,

How are these units wired? Are they direct to the battery with an inline fuse or are they through a few block?

Couple things.

First, ignore the CCA rating - That's cold cranking and only matters for starting at -18C... which I don't think you are doing. Focus on the CA (regular cranking amps) which is nearly identical for both batteries.

The low voltage warning might be a little premature. Do you have a digial multi-meter that can be used to measure right at the battery terminals and compare to your dash readings?

I have a pretty heavy filter on my dash to prevent the sonar interfering with the radio. But the filter drops a fair amount of voltage, and as a result I usually measure about 11.4V at the dash when the battery is 12.8V. So I usually just "add a volt" to what I read at the dash.

Considered putting two batteries in the boat?

No battery expert for sure but I had the same problem with my 50 Yamaha when I had my Humminbird wired to the starting battery. The juice required to start the engine dropped the voltage below the low voltage warning on the graph. In my case, it froze the graph and I had to restart it.

I solved the problem by adding a separate battery for lights, and electronics and switching from a 2 battery to a 3 battery onboard charging unit. When I plug in at home to charge the trolling motor batteries, the extra battery gets charged.

On my old Nitro I used to get low voltage warnings on my graphs all the time even though there was lots of juice to crank the engine. The wires that feed the dash and bow were tiny and there was too much of a voltage drop from battery to bow/dash. I rewired the graphs directly to the battery and the problem was solved.

Ed

Thanks, fella's - great input!!