Have not posted for many years. Rick Sheldon here Destin Fl. Retired old man, young at heart. Purchased a 2106DS a few yrs ago. Been working on installing Lithium batteries so I can run AC unit for 7 hrs. About finished after spending almost $8k on new equipment. Fell, hospital, surgery etc. Returned back to almost completed project. I have title in storage boxes so I need to know Mfg date. How can I find this?