First of all, a true livewell is not a requirement at our events. With the bass guys, however, that's a different story......
Now for your livewell, a dedicated group 31 marine deep cycle battery coupled with a true livewell switch &/or timer should keep you running most of the night provided you adjust the timer to activate every 20-30 min or so, depending on the timer of course. You might even be able to run your fishing lights off the same battery.
I'm not sure of your whole setup so maybe take a set back & look at your entire electrical needs and make improvements/changes from there. My two cents....
LLL