Doesn't start and shows "Failure..." on display
Hi, a couple of things you can do but may I first suggest you bring it back to the Technical Support people who replaced the battery and voice your issue. The new battery might have to be replaced (don't be surprised) and you may have certain warranty claims that may be void if you try opening the UPS yourself.
If for some reason you want to do it yourself, then you have to open the UPS and check the circuitry including the new battery. You need to be familiar with the use of a multitester (VOM), working with HOT circuits and general electronics. You have to start with any fuses, circuit breakers, relay, SCRs, transistors, etc. If you are not that comfortable doing so, guess were back to the first paragraph.
Hope this be of some help. Good luck