What specifically are you trying to benchmark? For example, is it runtime...
- Under normal usage? (so you know what the run time will be with the way you use the system?)
- Under optimal settings/usage? (so you know what the theoretical runtime can be if you dramatically modify your usage habits?)
- Under very heavy usage? (to see the worst case scenario?)
- Under highly-specific usage? (ex: streaming videos, listening to audio through the speakers, playing a specific game, so you know what to expect when using the system in a very specific manner, such as if you only stream when traveling, and while traveling you often don't have access to AC power?)
So here's my dorking out...
Before testing, one could reset the SMC and then use the battery for several partial discharge-recharge cycles. After completing that and shortly before beginning the actual testing, they could discharge the battery to say 90%, charge the battery to 100%, and give it several hours on AC power once it reaches 100% in the event that the 100% it reports does not actually correspond to a full charge (often with devices using a LiCo, 100% does not equal 100% and 0% almost never equals 0%.)
Normal usage to me is the most important single benchmark to take, especially when the system is newer.
You could use the computer normally as you would, at the brightness you normally would, using normal Apps, and continue to use this system until it gets to a set lower threshold (say 10-15% [1-5% places too much wear on lithium batteries IMO]) and then record the runtime. Do this a few times to establish an average, and you know your estimated runtime with your normal usage. If you really want to dork out, you can keep a spreadsheet noting the OS revision, OS-level settings like brightness, which Apps were running that had notable energy impact, what App revisions they were, and even notable background running tasks.) Later on, if runtime seems reduced, repeating this test can provide a nice comparison to try to determine if runtime has actually decreased, what factors might be different, and if the different factors offer a more probable explanation of the reduced runtime or if battery wear is the more likely culprit.
If you wanted to see the potential max, you could set the brightness to a much lower threshold than you normally would, quit all Apps you are not using, disable most of your startup processes that have a notable energy impact, and perform only tasks that have very low power consumption. Repeat this a few times and this is a better estimate of the potential capability. If you want to be super nuts about it, you could do a fresh install of macOS and then perform the test
when no 3rd party Apps are installed on the system that have background running processes. IMO, this is not a very useful thing to know unless one is going to modify their usage to mimic such settings (which I'm personally not willing to do).
The one benefit I can see to this is that performing this test when the system is brand new with a fresh install of macOS and then immediately after installing all of their own Apps performing the normal usage test in the paragraph above would allow a User to see how significantly their own usage patterns affects battery life - but, that said, how valuable knowing that is if one is not going to radically modify their usage habits is still debatable IMO.
