@Ibeflyinhigh
I was able to run my '17 AR190 with a completely stock stereo for as long as 8hrs and was able to restart the engine. The stock head unit doesn't pull much power, even and medium to high volume levels. I think it's like 12W a channel at full rip or something small like that. Just not much power to pull there in comparison to battery capacity.
I upgraded my speakers to Polk DB651s's, but kept the stock head unit. Many of the 24ft guys upgrade the Polks that come standard in the higher end boats, and sell these for next to nothing. I got mine for the cost of shipping from another forum member. They REALLY REALLY improve the sound from the stock head unit, and are a super easy upgrade. This change had no affect on battery life that I could tell.
I also added a Wetsounds Stealth 10 Ultra soundbar to the tower. It has an internal 200W amplifier, and connections are a simple 12v+, Ground, and Signal. It throws a LOT of sound out of the back of the boat when at anchor. Enough so, the wife is constantly telling me she can't chat with others while we're out there in the water. Tons and Tons of volume, but NO BASS. I mean none, zilch, zero, nada. Paid $550 for it, refurbished, from creativeaudio.net. Has served us extremely well for the last 3 seasons.
With stock head unit, upgraded speakers, and soundbar, I've run as long as 6hrs on the stock single battery and still restarted the engine without a problem. I carry a small jump pack with me, and have only ever had to use it on someone elses boat (and my truck). It's cheaper and easier than adding a second battery keeping in mind we're only turning over a 1.8L 4cyl, not a typical V8 car/marine engine here. IMO, two batteries (for the purpose of a stock stereo) is overkill and not needed. There are 101 other benefits to having a second battery, and if you need/want those benefits, no harm or foul. With the stock, or lightly modified) stereo, I've not had any reason to believe I need that second battery.
Overall, if you're on a budget, these two upgrades get you a TON of sound output from the mostly stock system, and you're under $600 total invested. Aside from possibly adding a single channel amp and a 10in sub this spring, I doubt we upgrade the stereo any further in this boat. The sub is really my idea, my wife thinks it's just fine the way it is. Also, I should note, we're NOT audiophiles. We like some music to be heard, and not have wonky rattles and such. We don't need tons and tons of power to wake the dead, just enough we can here it while underway, and while at anchor and swimming. If you want to be DJ for party cove, this setup isn't for you. If you want to have decent sound, that you can hear everywhere for not much money, I think this is about the best bang for your buck you can get.