mwsilvers wrote:
There are no user replaceable backup batteries on Canon EOS cameras
Yes, there are in many of them... Just not in some of the more recent models, such as the T5i. This model uses a battery incorporated in the main board, that recharges itself from the larger main battery and rarely needs replacement.
However, that small "date/time" battery has nothing to do with whether or not the camera displays anything on the rear LCD monitor screen. So, even if it were user-replaceable (which it's not on this particular EOS model), it would make no difference. If that small internal battery failed, the camera simply would reset to factory defaults every time the main battery were removed and you'd need to reset the date/time every time you power the camera up. (Note: removing the small time/date battery along with the main battery from other models is a means of "rebooting" the camera to clear most settings, including any that were made in error. AFAIK, that's not possible with the models like this with the time/date battery permanently built-in.)
OP,
Can you call up the menu on the rear LCD screen? If so, look to see if you have "Image Review" turned off. On most Canon you can set the camera to automatically display the last photo taken for some period of time... or turn it off entirely (which I do on my cameras because it saves a lot of battery power... plus it's no big deal to press a button to recall the most recent shot when I want to review it).
Either the Image Review or the Menu or the "Q" buttons also should immediately call up something on the LCD screen. For that matter, the Live View/Video button also should cause the camera to display on the rear LCD.
If that rear LCD screen remains blank no matter what you do, then the camera definitely needs repair.
But, it sounds as if you have Image Review and Menu showing up okay.
Try the Info button... that toggles through several different arrangements of what's shown on the rear LCD screen (and only displays info... doesn't allow access to change the settings, the way the "Q" or "quick access" button does).
If you have set something incorrectly, so that what you want to see isn't showing up on the rear screen... You can go into the menu and do a Reset there in two places. One resets just the custom functions. The other resets all the other menu settings to the factory defaults. The problem doing this is that you'll also lose many other things you've set.
Another possibility (that you probably should check first)... The T5i... like most Rebel series models... has A TON of highly automated modes. I do not shoot with a T5i and never use any of those modes on any of my cameras, but maybe if you have one of those set on the mode dial (which on the top left "shoulder" of the camera), that's preventing the Q button from displaying anything.
The "Green Box" (might have an "A+" in it) is extremely automated and overrides many things. It dictates how your AF will work, makes the flash pop-up automatically, only allows the camera to save JPEGs and more. It's WAAAAYYY more than just auto exposure. Since I never use it, I don't know for certain, but it's possible that in this "super automated" mode the Q screen won't display (because that mode doesn't allow you to make any settings).
If you have the Green Box mode selected, try changing to P (program) instead... This still gives you auto exposure, but allows you to set up other things as you see fit. Actually, setting it to Tv, Av or M also should allow the Q screen to display.