Deltran like Migitty Matt posted.
I use one on both the boat and motorcycle batteries. My last bike battery went all most 4 years before need replacement. That is twice the expected life for it.
In the boat, I have wired a fused pig tail to the battery. Ran the cord down the side of the boat interior (hidden) to the back. I have a couple of other things I plug in and just ran all of the plugs to one place. I just drop the charger in after eash use and plug the pig tail into it. Nice and easy, battery all way ready to go.