Interesting. I use plane jane V6 Rangers with the heavy duty suspension. And let them get old. (Just sold a 1988 Ranger this month that I had sitting for 6 years - clutch went or I would still be still be part of the fleet. Added some water to battery and charged it and it fired right up when the fellow came by to buy it. $450. The exterior looked brand new no dents no rust. Trucks get washed every day. Waxed every couple of months and never driven in the winter.) LOL
But what is the earliest you can be on a lawn re:noise? You have to put your ear up to my pumps to hear them. I have them on pressure switches so they only run when the trigger is pulled so on a 5000 ft sq lawn at 3 minutes of actual trigger pulled is not a lot of stress on a charging system. 3 minutes x 25 lawns is an hour and 15 minutes of actual electrical usage. I probably don't even need to leave the engine running but I've done it for 25 years so creature of habit. There is a psychological thing too. If engine is running, my windows can be down, doors unlocked the back hatch of my truck up an no one is going to screw around with my vehicle theft etc when I am in the back yard. (I rarely lock up maybe 2-3 times a year in a really bad neighborhood.) But I've never had a theft problem. We don't us WPs only Fert & Herb so I guess thats why we get away with it.