Boat battery issue

[ErikOffroad]

So I have a Yamaha ar190 boat and the charging system is not up to the job of supporting a aftermarket stereo system. The problem is I have a alpine pdx v9 amp on the boat and it completely depleates the batteries faster than the boat can recharge them. I in the past have solved this issue by running the boat entirely off one battery. Then I ran the amp off the second battery. I was using solar panels to recharge the battery when the boat was not in use. The issue now Is that I am dry docking the boat at a new marina and do not have access to enough sun lite to keep this battery charged. I was thinking about buying a lithium battery jump pack and using it to support the battery while in use. I found this one. I’m not sure if this will work as a solution to my problem or not.
https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/142591789144
It’s 4000amps which is more than some others I saw on the market. Idk if u guys had another suggestion or possibly a different jump pack that would work

 

[ErikOffroad]

Now that I think about it I think the battery in the boat is 850ah so 4000 maybe excessive

 

[Cornbread]

What kind of amp? My 2 digital amps in my boat don't use hardly any battery and it's no slouch of a sound system.

 

[Mike_H]

Bigger alternator, if possible... Is that Yamaha running jet ski engines?

Your other option might be to install a charger and have the marina plug it in when they rack it.

 

[ErikOffroad]

Ya it’s a jet ski engine. It’s a 1.8 liter single engine and there’s no belt drive so there’s no way to put a alternator on it.

There’s no plugs at the marina.

The only option I would have is to deplete the battery and then pull it and bring it home to charge. That’s why I was thinking about the lithium pack because it would be way lighter to travel with and I can charge it at home then bring it