The online manual show the battery in the tender. It also shows three screws to separate the boiler from the running gear...
The picture I posted was taken from the manual, it clearly shows the battery in the locomotive. You posted the manual for the later 3V board locomotive, not the 5V board model that is the topic of this conversation.
From this page: O Scale Premier 4-4-6-4 Q2 Steam Engine w/Proto-Sound 2.0
This is the manual that is linked.
MTH 20-3048-1 PREMIER 4-4-6-4 Q2 STEAM ENGINE OPERATING INSTRUCTIONS
This is a picture from that manual.
My Q2, 20-3048-1, shows the same manual on line at the MTH website, with the battery in the boiler. My locomotive is 5 volt, as it has no charging port at all. But...the battery, now a BCR, is located in the tender, not in the boiler as shown in the manual.
If my engine was 3 volt, I wouldn't have chimed in on the subject. The manual I looked up just happened to show the battery in the tender, where it was located on my 5v Q2, so that is why I posted it.
I recall I went the route of following the original manual data found on line, and opened up the boiler, only to find no battery or connection. My engine didn't come with a paper manual. The second manual search results, showed the battery in the tender, so I used that one for reference, even though it was the 3v version.
The only intention of mine was to illustrate that the battery on my 5v was located in the tender, not to prove any individual as being mistaken....