Baubatallion:
Luftwaffe engineering units (Pionier) or Construction units.
maybe this can be of some help with German Army/Luftwaffe abbreviations and acronyms.
http://home.clara.net/percy/glossary.htm
ZEL 306:
Zentral-Ersatz-Lager 306
=Central Spare Parts Depot
and this one was in Aal with branchlets in Drontheim and Moen.
Werner