I am going to eat my words on this point. A 2a maintainer should not be used as a charger. I bought a 2a maintainer for my truck, as it sits in my pole building since I work remote. Since they use those universal two prong connectors, or put a connector on my vintage ATV, and one on my deep cycle in a boat a was restoring. (until I wanted to invest in an onboard charger) and my motorcycle already had one for heated clothing.
Towards the end of the season, I was having starting issues on my fishing boat. And come to find the maintainer, was not putting any real charge on the battery, but would keep it topped, if it started that way. (obvious purpose of the maintainer) But I put it on my motorcycle this spring, to be sure it was ready for an upcoming 60 degree day, and it would not put a charge on enough to start the high compression twin. I had to use a standard charger to do so. But it worked good on my truck and atv, that don't have much parasitic drain.
I put some money into a good Noco dual bank charger and a dedicated crank battery in my fishing boat and all is good. Point being, if you truly want to charge, don't go below 5a per bank, and better yet, put in 10a per bank if running any deep cycle or need an overnight charge on a deep drain.
Good luck,