Something I apparently don't know, but what's special about the FJR battery?
The Deltran Bettery Tender Jr. is the same battery "tender" I use, I've had it about 4-5 years now.
For long term battery storage (which for me is the winter season, sometime in November - early/mid March, or so), I pull the battery out of the bike and keep it in my heated garage workshop, which I keep heated to around 62 degrees or so. Once a month I'll take an afternoon when I'm in the workshop, hook up the Tender Jr, and let it charge for a few hours. It actually shows a full charge pretty quickly, within maybe 30 minutes or so, give or take.
With my storage method, I don't think it's necessary to have it be in a constant state of charging (i.e. hooked up indefinitely and allowing the smart charging device to monitor and top-off as needed). Batteries sit in long term storage waiting to be bought without chargers attached to them, and having the Tender plugged in and hooked up is constantly using the electricity you are buying from the utility provider. In my very non-expert opinion, having the battery stored out of extreme cold means more than having a trickle charger of any kind constantly hooked up. I think periodic top-off with the Tender should be fine for you. But here's an extensive FAQ from their site, looks like it should be fine to do this-
https://batterytender.com/resources/frequently-asked-questions One of the points they make is not to ignore a battery being kept on their chargers, "just in case..." Lots of good info here.
Also, and I can't recall where I read this, but there could be unwanted affects to keeping a battery in a constant, long-term state of recharge, but before putting faith in this statement, I'd try to do more research for yourself.