80stech, I have my vehicles all connected to a battery tender about 80% of the time when parked at home (more, if for my e31), as when I drive, I sadly so not drive it far enough distances at high enough speed to properly allow the vehicle's charging system do its thing. you may NOT need to have your vehicles connected to the tenders as much as its all dependant on a few items (read below).

I used to live about 35 mins drive away, at highway speeds, from my office and my mech always said, when I lived that far of a drive, each way, that he had never seen a car with a healthier engine and battery... I NEVER knew whatr he meant about that until I moved into a house which is now a 7 min drive from my office and began experiencing bad battery issues and engine oil "mayo" in all 3 vehicles. then it dawned on me that since I'm only driving SLOW, SMALL distances, it affects my vehicles 2 fold.

1) My charging system is not getting to recharge a battery, so over the weeks/months, the battery voltage was slowly dropping since I wasn't connecting it to the C-Tec charger religiously, (as I used to only use it when on vacation or vehicle was in storage)
&
2) the engine oil temp was not getting up to proper heat for a long time to burn off the condensation that builds up in a engine from short trips and especially from cold exterior weather temps. So I was getting the deadly "mayo" buildup in the valve covers, oil return lines and under the oil cap (thats the dead give away sign you have an issue) - obviously that problem can't be solved with a battery tender.

So now I have to choose which vehicle I drive. 4 cyl, 8 cyl or 12 cyl based on weather temps, conditions AND distances I'm going.

BUT ultimately, when I park my vehicles (at home), I open the bonnet, connect the C_Tek charger cables to engine bay battery leads and remove the oil filler cap, to allow any heat/condensation to leave and potentially avoid "mayo" buildup.
Overkill for a lot of people, but I'm fine with this VERY QUICK procedure. Hell even when I drive my vehicles to my office (underground heated parkade), I've often removed the engine oil cap and left it on the drivers seat, so the small moist warm air can escape the engine oil system.

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I swear, my cars are like a girlfriend.
Sometimes its a rough ride, sometimes its smooth motorin'.
Sometimes she doesnt like how i treat her and sometimes i dont like how she behaves.
BUT at the end of the day, she loves it when I am inside her.

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'91 850i
'05 X5 4.4i
'09 Clubman S