Nether will a UPS. A genset is the only long term solution. Need automatic, then invest in a small standy unit. In the real world we use UPS system to hold a load over for 5 to 15 oseconds, after which the gender is up to revs and can take the load. Worst case, the UPS needs to hold the loads long enough for automatic shutdown, maybe 10 minutes max. The extended runtime units are usually secondary to the main UPS systems and placed on critical loads that need safe shutdown. Using a UPS to provide backup power for high current loads is silly and costly.