Vehicles are frustrating...

[Chase31]

You shouldn't have to replace the batt and the starter. Should be one or the other. Sounds like something else is going on

[spit.fire]

the starter was on its way out and the battery is toast from sitting for too long without ever charging it

[hillegom]

Yes, if you don't use a battery, it must be charged, minimum every 6 weeks.
Batteries always self discharge. These days you have a computer and a radio which have parasitic draws.

You can now buy chargers that vary the frequency of the voltage so that some of the lead sulfate will fall off/get dissolved into the sulfuric acid.
Bring your battery to me and we will find out if this works. Not all batteries will be rejuvenated.
Cost you a frag only if it works lol