I use a trickle charger occasionally, generally only if I get an excessive battery discharge warning. My car tends to sit idle for as much as a week at a time (I'm away a lot), and the car is mostly used for relatively short trips - less than 10 miles usually - so the battery is often not fully charged. I throw the trickle charger on overnight and that fixes it.
E93 335i convertible, F15 X5 xDrive35i
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