The gripe that I have with every "smart" charger that I've ever owned or used is that they will not charge a battery that's 100% dead. If it doesn't read voltage from the battery when it is initially connected, the logic refuses to turn on the charge voltage for safety reasons.
I have an old 1970's lump of a transformer-based 5/10A charger in our garage, and it seems to get more use than all of our "smart" chargers combined just from resurrecting batteries from the dead just so the "smart" chargers can take over.....
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Currently BMW-less. 
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