Well, I never got that ‘new math’ they were teaching many moons ago 😂

I'm not sure if but they've ran music fairly well the past 5 years but noticed past couple summers they'd start to drain by end of day. I believe they are both the same size. I'm thinking i'll just have to eventually invest in 2 more strong batteries. Thanks for the tip on lead/agm!

Are they both "starter" batteries? At 5 yrs old they will likely need replacing anyway, so you could do one starter battery and one deep cycle - it wont have as much cranking capability but far more amp hour capacity for tunes.

Just be sure both are lead acid or both are AGM, dont mix and match as they charge differently 

It would have to be a very serious leak before I would consider cutting up the tank to remove it.  How much water is leaking, or how long does it take for the bow tank to go from 100% full to 50% full?

3 hours ago, Josh7711 said:

Thank you in advance for any help. What can I do to make sure I have enough battery to push best sound all day and not end up draining both batteries? I have a 2018 Malibu MLX. (purchased new in summer 2019) It has 120 hours on it and same 2 batteries that came with boat. I play music on either battery 1 or 2 then switch when it's time to go or battery starts fading. We'll be playing a lot of music this weekend and have a feeling we'll be using a lot of the battery. I have a portable charger in case engine won't start when departing. Sometimes the base and or certain speakers will shut off if battery is low. What can I do to make sure I have enough battery to push best sound all day and not end up draining both batteries? Is my only option purchasing more robust batteries? Thank you for any help!

Three ideas 

Add more battery

Spend more time charging

Or less use 

My limited understanding of regular lead acid batteries is that frequent deeply discharge will shorten the lifespan.