I say get the Sam's Group 31 AGM for the main boat battery. You want to be able to start that outboard after running 2 sonar units all day along with livewell pumps, etc. You might get by with the Group 27 AGM, but you'll have a lot of peace of mind with the Group 31 (instead of the Group 34 you had). For the TM, you should be just fine with 2 of the Group 27 Deep Cycle batteries (the black ones). Those are ~$83, have good specs, and will save you some $ and a few pounds vs. the Goup 31s that I think would be unnecessary for the TM. You will need to check the wet-cell batteries every couple of months for electrolyte level to learn if you can go a little longer between checks. (Only used distilled water in them, and learn what the proper fill level is if you aren't familiar with how battery filling works.) The ones I have with an 80# thrust motor can go 3-4 months between checks, with my particular charger. You don't want a charger that's going to "boil them out" as that ruins batteries.

Update: I did learn that Yamaha is "playing it safe" in saying don't use anything other than conventional flooded cell batteries with their outboards. I view this as more of a CYA to weasel out of any unpredictable issues. My personal choice would be to go with the AGM anyway. If someone here knows that yammys have an issue with AGM, please speak up.....

I did find the minimum battery specs provided by yammy for a 200hp 2-stroke:
380 CCA (502 MCA)
124 RC @ 25 AMPS
70 AH @ 20 AH RATE

Min. specs for yammy 200hp 4-stroke:
512 CCA (675 MCA)
182 RC @ 25 AMPS
100 AH @ 20 AH RATE

The $159 Group 27 AGM Sam's Club battery has the following specs that exceed what Yamaha 2-stroke calls for (which I like and would probably be fine now that I found your engine requirements). This one is a bit weak ion RC and AH if you have a 200hp 4-stroke.
Battery purpose: starting/deep cycle
20 amp hour rate: 92
CCA at 0 degrees F: 580
MCA at 32 degrees F: 900
Reserve capacity: 175

What kind of battery for a yammy 115 4 stroke?

On application charts I see the following footnote concerning Yamaha 4 stroke engines, including yours: "Yamaha recommends a cranking-type battery that can have distilled water added to its cells when necessary. Maintenance-Free, sealed, or Gel batteries are not recommended because they may not be compatible with Yamaha's charging system."

So, if you want to follow what Yamaha says, you should stay with traditional flooded cell batteries. The MINIMUM specs for the yammy 115 are documented as:
380 CCA or 502 MCA (CCA is rated at 0 degrees, MCA is rated at 32 degrees)
124 RC (@ 25 AMPS)
70 AH (@ 20 AH RATE)

Sam's has an $80 kick-butt Group 24 marine battery battery with the following specs that exceed what yammy says you need, and is they type battery they want you to use.
CCA at 0 degrees F:840
MCA at 32 degrees F:1050
Reserve Capacity:182
Sam's Group 24 Marine Starting Battery

They are at a great price. They have 105 amp hours. They will run the trolling motor as long as anything out there. Last set lasted 6 years. Only downside is that they are heavy.


Deep cycle batteries aren’t made for outboards. For that cold cranking amps are more important. That’s not what deep cycle batteries are made for. They are made for longer steady current drain. So for a outboard make sure the battery is at least rated dual purpose.

Just replaced my starting battery yesterday with another Exide AGM Group 24 from Academy. Old one completely caput but still had original receipt from 2013 so not complaining to get that much use. That said not real cheap at $179.

Listen to this man ^^^^^^ he is a wealth of knowledge. Was kind enough to spend an hour with me on the phone talking batteries etc.. VERY helpful and VERY knowledgeable.

Thank you sir!!!!

Thank you, Frank. I wish I knew "catchin' " as well as I know electrical!

You could have gotten the whooping Group 31 AGM for that price at Sam's Club. Huge difference!

Mostly true. The Duracell AGM is $180. For TM use, the Duracell Deep Cycle battery (flooded cell, Group 31) is also 105 AH, but comes in at a much lighter $100 price tag! It also weighs a few pounds less. AGM is fantastic for heavy amps (like starting), but for deep cycle, not really any better when comparing to equal counterparts in flooded cell. The bottom line is you spend $80 to avoid having to check the electrolyte level every 2-3 months.

Also the Duracell AGM 31 isn't big enough in terms of CCA for most new 250's plus all the stuff guys are running. 4 graphs, poles, pumps, aerators all day etc. The Odyssey, X2, Northstar are best I've found for the dual purpose stuff.

As far as Mercury spec, that's as follows: MCA: 800 Reserve Capacity: 135 Minutes (@ 25 Amps, which is the traditional measure for RC)
The Duracell AGM Group 31 is: MCA :1000, AH: 105, RC: 210.minutes

I looked up the Northstar Group 31 at their website (NSB-AGM31) and found the following:
MCA: 1350, AH: 103, RC: 220 minutes
So, the Northstar can provide more high-discharge amps to start a really big motor, but not really a bit more deep cycle capability than the Duracell (made by East Penn I believe).

As far as cranking a Merc, the Duracell AGM is more than adequate, well above minimum. Poles? Power-pole says a 55AH battery will cycle a pole 1200 times, yes, 1200 times. I'm betting most don't cycle (a pair) more than 50 times in a typical fishing trip, on average. You mention "aerators, pumps", where both are pumps (4 total) but it's rare to keep running fill pumps constantly in addition to aerator pumps - why would you?

Based on numerous comments here, I'd gather that quite a few do just fine with their rig and a Group 31 AGM as I do (3 graphs, structure scan, plus more), even with the "lowly Duracell" that really isn't much different than premium price branded batteries. One group may manage their power better than the group that has issues.
The gotcha is running 4 big graphs + livewell pumps + who knows what else NONSTOP from the moment the hull gets wet.
Nonstop usually isn't necessary for 4 graphs simultaneously. There may be other things some turn on once and leave on all day, need it or not, then complain about their battery. I bet most of them have no clue what sleep mode is for a graph as my experience has been few ever let daylight see the inside of an owner's manual. You can't sit at the console AND be at the bow, but I guess it looks way cool to never use that sleep function I bet many have never tried. (Sleep allows the unit to come back up to full function without a reboot.) As Jeff Foxworthy says "Y'all turn something off!" (when it doesn't really have to be on) and I'd be surprised if you can't "get by" with a Group 31 AGM with the specs of the Duracell unit. For the rest, Honda sells some rather quiet generators.....

As a courtesy, please point out the 250 that requires more than 1000 MCA.

Thank you so much!!! I am learning about all this as I go and you have taught me a ton...I appreciate you taking the time to inform me properly. I am a first time boat owner and currently trying to get my boat set up exactly how I want it. You have saved me from some future frustration for sure. I will go with your suggestion for sure.

The Duracell just wasn't enough at the end of the day for us. It's a great TM battery but just wouldn't hold up once you had all electronics and accessories drawing from it. The Odyssey pc2150m is perfect for our application

I think the view is subjective, just as some are convinced that their "brand" is better in the Ford vs. Chevy argument.
The battery you are tickled with has no more Reserve Capacity or AH rating than the Duracell AGM. In fact, that particular Odyssey rates ever so slightly lower on BOTH of those specs.