Cadillacs, like other GM vehicles do not usually have battery, charging issues. The problems with draining batteries while working on interiors usually results from the detailer constantly opening, closing and re-opening the doors again. The key with all GM vehicles is to simply open all of the doors and keep them open the entire time you are working on the interior. If you keep the doors open then you will notice that the interior lights will usually go off after about 15 to 20 minutes.
Just open the doors once when you are ready to do the interior and keep them open.