Or get something sold for off-grid use instead of as a UPS. Ecoflow is one of many vendors.

We have widely deployed the workstation devices and have had no maintenance issues. we installed ~10 9PX models and have had 2 fail suddenly and completely just out of warranty and one with a failed battery charger, also just out of warranty, and a gigabit management card that works for a week or so then goes offline and requires local reboot from console but we have about 10 deployed with no issues too, so buy extended support because their support team is good but useless if you don't pay the protection money. We also had a rack PDU just die right out side it's warranty phase and we only bought 6. Not great quality it seems but it does the job. We had one install of a full rack UPS and it's been running for more than 7 years, but you have to keep the maintenance up and schedule battery swaps. They do make a really nice 1U lithium-ION ups also which is neat. The IPM software is a little janky but also works well.