You’re killing your car. Starting a diesel letting it idle for 20 mins to warm up. Then revving it high to blow out the cobwebs is causing nothing but problems. If you’re not using it, don’t use it. Slightly over inflate the tyres then leave it alone if it’s just six month. Then when you put it back on the road buy a new battery or second hand from a scrap yard and drive it normally for about and hour. Mostly under load.(Not revving it, at motorway speeds normally). It’ll be fine…. I’m a mechanic btw