Potentially bad 12v battery experience

We have found some experimental evidence that may be related to the
Smart car battery "bricking" issue.

Bill, a forum member, reached out reporting a phantom power drain in
his 2015 451ED. It was sometimes losing 10% charge overnight and he
was trying to chase it down. Both his high voltage and low voltage
(12V) batteries were original to the car.

After some investigation, it appears that the car was frequently
charging the LV battery from the HV battery and this was likely the
source of his phantom power loss. If left to continue unchecked, this
is also a possible source of the smart's "bricking" problem.

The generic Group 47 battery ($105 at Costco) is about an inch longer
than the old original battery, but it slid into place just fine. The
only problem is that the original hold down clamp would not go into
position. A little hacksaw work on it allowed it to do its job again.
There is a sticky near the top of the forum giving installation instructions.

More details in the next post about the data collected along the way,
which you can skip if you're not interested, but the takeaways for us
are:

If you notice an unexplained power drain on your HV battery, you need
to find out why.

If your battery is five years old or older, you should keep an eye on
it.

If you have a multi-meter or a battery test unit, you should check
the 12v battery every once in a while, more often if either of the
first two issues are yours.

Good luck. Hopefully this experience will help a few owners from owning
a "bricked" Smart car.

Len, Bill, and Jim