2020 Ford Fusion Hybrid Battery Health Test

I am looking at a 2020 Ford Fusion Hybrid that
has been sitting on the lot for 10 months now.
The dealer seemed surprised I ask about battery
health. When I went to test drive it, the 12V
battery was dead. I know this has nothing to do
with the Lithium Ion hybrid batteries, but it got
me thinking - how long can the Fusion sit before
these batteries are damaged also? Is it possible
to run a diagnostic test to verify battery health
and capacity? And lastly what would a
successful outcome of that test look like? The
dealer is claiming they can run a test, but that I
need to come to some agreement first since it
will cost them money. Thanks for any help!