Any generic trickle charger will work fine. I personally prefer the charger/maintainer combos. They're not that much more if at all and you can charge a battery if needed whereas the trickle chargers could take days. They have smart ones that will do bikes, cars, lithium, etc. and do deep cycle, blah blah blah.

This guy, for example works well for me:

https://www.amazon.com/gp/product/B07ZVRFX2M/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

PS: Yes, the proprietary connector is annoying. there are others with standard connectors.