Boat came with two starting batteries and need to replace one for house.....HELP!

[Kahuna Khris]

I have been getting low voltage warnings on my 2016 FSH Sport boat gauge (with alarm) and low voltage warnings on my Humminbird fishfinder as well. I have to turn on the parallel isolation switch to temporarily resolve the issue. I tested the batteries and the start battery was low (8.5 V) while the house battery (an identical battery) seemed fine. I had the start battery tested and am replacing it as it failed the load test. My issue is this......When I pulled the start battery, which is a starting battery, I noticed that the house battery is also a starting battery. Shouldn't the house battery be a deep cycle? I want to replace both at the same time but am not sure if they are the same due to charging requirements etc. I was just going to replace them with two starting batteries, as that is what the dealership installed, but then noticed this post that Tonka's came with two deep cycle batteries. HELP!! I have lost faith in the dealership's opinion as I have learned over the years that I know more about this boat than they do. Neither of these batteries are used to power my 36V Riptide as I have 3 dedicated batteries and charging system for them. House battery used for Humminbird, radio and Canon Mag 10 downriggers. Boat motor is off when I use this equipment as I can troll with the Riptide.
Batteries are both Napa Marine 24M-7, (800 cca /1000 ca) starting batteries (see pics below). They are approximately 2 1/2 years old.

So I don't want my question to get lost in all of the background. Should I install a starting battery as the start battery and a deep cycle as the house battery? If so, do they have to have identical ratings and will my charging system (boat alternator) be OK with the two different batteries?

Opinions please.

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[MIDLIFECRISIS]

Your charging system will be fine. I also have 2 start batts. The next time I change batts I will get a start and a deep cell because I have installed a refrigerator in the boat.

 

[Jaylex]

I saw a similar post where the dealer installed 2 starting batteries....low batt signal came on...eventually swapped one for deep cycle and it solved the issue.

After 2 1/2 yrs that start battery has likely lost 50-70% of its capacity...maybe less but since it's not rated to be depleted past a certain point each subsequent charge reduces its capacity if I recall correctly...

I have 4 amps and 3k watts and use 2 deep cycle group 29 batteries with no issues.

If u replace them get at least a group 27 or 29 deep cycle so you can properly run your equipment when the boat is off and recharge them without degradation.

How often are u charging them after each use?

My first boat had 3 amps and I fried my first set of interstate batteries, by not consistently charging them between uses, since adding a battery tender and regularly charging I've had no issues.