What does this UPS battery error mean?

Battery is dead. It will not support load. Your UPS is now a surge protector until the battery can be replaced.

Is it safe to leave in the condition until we receive the parts?

That would depend on what it's protecting, if you loose power it's going to drop like a rock

Personally I wouldn't run the UPS in this state for too long.

If it's going to be longer than a few days, my suggestion would be to power down what ever it's protecting, put the item(s) on a good surge protector and power off the UPS until you can get good batteries installed.

Changing the batteries isn't rocket science though some models do make it more annoying than others in my experience

The local Menards, Home Depot, Lowes, Fleet Farm, Tractor Supply or Walmart usually has these batteries for a reasonable price.  They're either a motorcycle or garden tractor battery.  If time is not pressing they can usually be obtained from fleabay for less than the local price, but ... fleabay prices often mean fleabay quality.

In most cases you unplug the UPS (input and output), unscrew the battery door cover, and then the battery swaps out by unplugging two spade lugs.  Be sure to get the appropriate connectors when buying a battery, as there at three different types (post, screw and lugs).

It's prudent to check the electrolyte level in these "sealed" lead-acid cells yearly.   They're claimed to be maintenance-free, but that's true only as long as you don't mind replacing them every three years.  The constant float charging tends to electrolyze the water rapidly.  In most cases the "sealed" caps can be popped off with a box opener, allowing replacement of the missing (distilled) water.

Speaking from experience when I ended up in hospital for 3 days on oxygen with hydrogen sulphide poisoning from an APC UPS with a battery fault condition like that!

If anyone is interested in the full details let me know!!!

IT IS NOT SAFE AND NEEDS ISOLATING AND REMOVAL FROM AC IMMEDIATELY!!!

Do you have Smart-UPS connected to monitors so you can check alerts and battery temps?

Also if you leave faulty batteries in APC UPS they can overheat and warp and you cannot remove as they swell up!

APC only now warrants battery life for 2 years so how old is the UPS and it’s battery!!

It maybe time to change the UPS and not just replace the battery!!!