Adam, if it is just the running lights consider replacing them with LED running lights and an LED anchor light. They cut your power consumption so much that despite the high price (of good ones) they can be the cheapest way to make your battery bigger.
Then throw on a small solar panel (that is warranteed for exterior use in the rain!) so the battery will stay topped up when the boat is not in use. And maybe a GFI, a long extension cord and cheap charger as "trip insurance" you can use at docks.
Odds are if you switch to LED lighting and the battery is any good to start with, you'll be OK.