You can contact your local power company and ask for your representative to come and visit you. Your representative can also provide you with the formula for conversion plus provide information concerning meters, etc. to help you track your cost during all shifts.
Once you have met with your power company representative, make sure you ask if your power company has a energy conservation program available and seek assistance for tracking a help saving your company operation cost reduction program such as energy efficient equipment etc. Use their engineers to help.

You might even want to consider going to fuel cell Hydricity power packs that triple runtimes and just drop straight in. Allows you to do away with all the charging paraphernalia.

I would contact Industrial Battery Products, they are an excellent organization that can definetly help you. 630-679-2271