The good news is your UPS came online as soon as the power went out. The bad news is it dropped the load almost as quickly. The plant manager, furious, announced that he'll be holding the UPS manufacturer responsible, saying “Their product obviously doesn't work as advertised.” However, you know the fault probably isn't with the UPS itself, and you want to solve the actual problem so the load doesn't drop in the future. So you ask your boss to wait until you've been able to conduct battery testing. He replies, “We sent a tech out there with a hydrometer, and the batteries are good.” What troubleshooting should you do?
The hydrometer readings don't tell you the condition of the battery; they just indicate the specific gravity of the electrolyte. You could have depleted plates, but still show “good” on the hydrometer. It's like checking your tire pressure to see if your car needs an oil change.
Your first task is to analyze the battery monitor logs. If you don't know what you're looking at, contact a battery maintenance consultant so you don't end up making expensive mistakes due to misinterpretation.
Improper maintenance is usually the cause of premature battery failure, so determine if maintenance fell short. Review the maintenance logs against IEEE Standard 450, “Recommended Practice for Maintenance, Testing, and Replacement of Vented Lead-Acid Batteries for Stationary Applications.” (Reference the manufacturer's recommendations if you have VRLA batteries). Test your batteries to determine their actual condition. If you don't have an internal resistance tester, you probably don't know how to test batteries. Hire a qualified firm to conduct the testing.
When your boss has the results of this troubleshooting, he can then make a good business decision about how to proceed. Not before.