NOCO GENIUS5: 5A 6V/12V Smart Battery Charger – Automatic Maintainer, Trickle Charger & Desulfator with Overcharge Protection & Temperature Compensation – for Lead-Acid & Lithium Batteries

Since you already have a harbor freight charger, here's the cheapest one that is a real charger: https://www.harborfreight.com/2-amp-612v-3-stage-microprocessor-controlled-automatic-battery-charger-57015.html On the opposite end of the spectrum here's a "name brand" nice one that would likely meet all your need forever as long as you don't need an expensive really fast charger: https://a.co/d/00jkwcCf If you want a faster one, just go up in that same series e.g. noco genius 10

Instead of purchasing a new battery go with a Desulfator charger, which can Frankenstein a dead battery back to life. And not only is this a killer charger, it can also charge lithium batteries (which means it can handle the Yuasa AGM or the Anti Gravity. https://www.amazon.com/dp/B07W8KJH44/?coliid=I1053P4OU1M3UT&colid=37H4GHU4ZL9EQ&ref_=list_c_wl_lv_ov_lig_dp_it&th=1