Catch if the files needed in the battery module are missing and exit early. Do not mess up the bar by printing error messages. Instead abort.
/usr/bin/env
To increase the portability (OSX for example has zsh under `/bin/zsh`).
Replace all occurrences of [ with [[ in bash and zsh scripts and configs. Performance wise it makes sense to use the builtin instead of calling an external command also when from a functionality stand point `test` would suffice.
