For comparing those brands (EcoFlow, Anker, Jackery), you might want to check the wh/$ ratio - it's basically the best way to compare power station value (for newer LFP systems). I went through this same analysis recently - gearscouts.com [1] has a pretty good comparison table that tracks actual street prices vs capacity.

I've found the sweet spot is usually in the 500-1000Wh range for emergency backup. Enough to run a fridge for 8-12 hours but not so big that the solar panel costs get crazy. The LFP (LiFePO4) models tend to last way longer than the regular lithium ones - worth the extra cost if you're planning to use it regularly.

Your lawn mower experiment sounds like it was a good learning experience! Those small Harbor Freight panels are great for tinkering. I started with something similar before going to a full house system.

[1] https://gearscouts.com/power-stations