I am using a $30.99 from 1800emart. The top came off and I told the guy I thought he should replace it. So he says as soon as mine arrives, it has been mailed, he will mail me a new one. If he holds true he is a stand-up guy.
SD rule of thumb is 1 amp per hour's running with two 48 volt phantom powered mics. I would shave an hour off the total to be safe and always carry a spare.
Cheers