Here are reference photos of that area from two model kits:


The second photo has the exhaust, so that would mean it has the UAAPU. Note that the panels are the same. I reckon the difference between a tank with the Hawker battery system from a tank with a UAAPU is that the latter has an exhaust whereas the former does not. Also note that the difference might also be because these could be two different models from two different manufacturers. The first could be a Tamiya kit, the second would be the Dragon kit. Anyhow, what is important here is how the panels on the deck look like.
Removing the fuel cap is easy. All you need is a razor saw. Then just scribe the panel lines like I did. Just add an exhaust to make yours look like it has an UAAPU.