It would be interesting to put a battery charger/starter on the existing battery and see if it starts.
If so then what Isaac-1 said will be proven true and you may need to buy a new battery.
2004 Monaco La Palma 36DBD, W22, 8.1, 7.1 MPG
2000 LEXUS RX300 FWD 22MPG 4020 LBS
Never blame someone else for the road you're on.
That's your own asphalt.