I never heard of the dangers of trying to kill the engine via key as opposed to button. While we're doing it less and less as time goes by, we most recently did it two days ago, and we've certainly done it 50 times or more in the last 4 years.
With regard to boiling off batteries with the chargers, this should only happen if one or more of the chargers is damaged or set incorrectly. For years we used to leave both chargers on at all times, with no ill effects at all.
We still activate both chargers at the same time for limited time periods.
SM2K N° 350