Here are a couple thoughts my co-hart instructor at class (automotive technology) and I have had. Anyone notice there are no more 5 year auto batteries? Remember the "Die Hard" battery commercials about how long they lasted? Even a 3yr battery is hard to find, most are 2yr now. Reason? With what info he came back with from a conference this last summer, lead acid type batteries are on their way out. AGM type are the way of the future, or gel types. So I would see if maybe there is a "dual charge" type available if you plan on keeping it forever like I do. Or the other option is, just get one to carry you thru for say 5yr or so and not invest a bunch of cash.
I still have my tried and true 2/8 amp "Die Hard" little battery charger my wife got me some 40 yr ago now probably. Here is one I just looked up that will cover you for a very long time. About $84. Way above my allowance, but I don't know what your budgetary commissioner will allow. Or if you have a Horrible Freight close by this one is $30