Sounds like the usual "stealership" rip off BS ! 
IMHO, even if any built up pressure did not come out thru a dipstick tube, etc., you would blow out a seal before blowing out the tranny case aluminum casting!! Did any battery acid go into the tranny? I would think positive pressure from your tranny vent tube would prevent that, but if so flush the tranny.
Are you having problems with the tranny or drivability of ther car? Give us more info; symptoms,problems,etc. Can understand your rage, but calm cool thinking with more info will be far more productive for you and will better allow the members to try and help you.
