Batteries are ultimately at this time not a lifetime purchase but you can buy 10yr warranty lithium batteries. Look at ohhmu, battle born, Dakota lithium for example. You do have to be cognizant of cycles and discharge / storage levels / etc.
edit not to be as negative and I misread A/C unit as A/C outlet for some reason:
Since this has been a couple years -
I think you mean kVA which is very different than KV. Panels, charge controllers, batteries and invertors are much cheaper. 10yr Lithium batteries can be had for 100-150ah for...