As a Boat Detailing Specialist, you may want to offer services such as making sure your clients' boat's batteries are charged and offering to charge them or test the boat before they arrive for their departure. This is an easy service to provide and will keep you on the top of the boat owners list of reputable and reliable service companies. Battery Chargers can be purchased at:

http://www.exocache.ishophere.com/shop/list/9/start.html

You may offer to stock the vessel