
It's not the temperature, it's the karma.  You see, dirt has good karma,
since it's all organic and full of living things, but cement is all squared
off and artificial looking, and has lost its karma in the process.  Being
a karma sink, it sucks all of the good karma out of the battery which is no
longer able to keep a charge.  Because wood is also good and organic, putting
a board between the battery and the cement will fix the problems.