Battery warmer

[coatings03]

hellow fellow barners, i had an experience with cold weather approx 42 degrees with my 29 speedster. I had it covered as we had a cold spell in southen Calif.
my 6 volt battery was dead after 2 days. I charged it up and it was fine. I have seen these battery warmer that are pluged in keeping the battery at 70 degrees.

any experience with these units?

thanks,
jim m