Try a few of https://www.amazon.com/Power-Sonic-PTX20HLBS-FS-Powersport-Motorcycle/dp/B07B1L15W3/ in series (each gives about 240W of power, series adds Ah while parallel adds V so to reach 300w two in series and two in parallel should work [24v @ 40Ah] given a solar or other input since 40Ah will be spent in minutes ).

20 years ago a few frends and I used about five https://www.amazon.com/Optima-Batteries-8016-103-BlueTop-Starting/dp/B00075OSCO to run a rig for Unreal tournament offgrid (about 650W) with a solar panel.