First, you must have a partially charged, recognized battery to install any BIOS update.  Once that's in place, if A16 still won't load: There are multiple earlier versions between A06 (and after A16) -- try installing one of the earlier versions, starting with A07.  One or more of them may be needed before A16 will load (click on "older versions" under BIOS below). [URL]  
I have a Dell Latitude 3450 and it has no battery. My BIOS Version/Date is : Dell Inc. A06, 7/6/2015. I went to check updates and found dell bios update and it was critical. When I tried to install it, nothing happened. I think its because of the no battery but I tried to force it using CMD. Still nothing happened. The latest bios version is A16 22 Feb 2018 for Dell latitude 3450. Please Help.  
Latitude 3450 bios update wont happen