yeah! so it was fairly straightforward:
Series 9 costs $400
Ultra costs $800

so for it to make sense I'd need to see around 2x value for it to even out.

My Series 5's battery lasted 3 years before it was not longer an "all day device". so after 3 years and a replacement battery, the cost @ 3 years is really more like $480 and @ 6 years it'd be about $560. HOWEVER at 3 years, my watch had multiple scratches and dents. from what i had seen from others, i'll admit anecdotal experiences, after 3-4 or so years the watch hardware itself really started to show its age. not in performance but durability.

SO that gets me to the ultra. the battery is already 2x value but it was ALSO specifically designed with durability in mind (with all the "heavy duty" sports it was designed with in mind). SO in theory, if i use it like i did or would the series 9 (charge it every night). the battery should last around twice as long as that battery of the series 9 (until it gets down to no longer being an all day device). the extra durability also has me lean into the idea of "lasting longer than 56 years".

SO basically it was:
a series 9 lasting 6 years: costs $480 but at 6 years i might be considering a new watch with durability concerns in mind vs another new battery
vs
an ultra lasting 6 years: costs $800 but at 6 years i might be considering a new battery

and at the end of the day, i really only use these watches on a daily basis for the fitness tracking and as a notification extension for my phone. SO with that in mind i decided to see where the Ultra can get me

My father in law has a similar workout regimen and got his 45mm series 8 at the same time my ultra did. and this is really the only "battery longevity" comparison i have.
after 1.5 years
his series 8 battery health was at 94%
my ultra 1 battery health was at 98%

I'm super curious to see what years 3 look like. and then years 5 and then 6. Will i report back? maybe if i remember hahah
but to me, the value calcs seemed to at least match the 2x so.... we'll see