as mike said, if its for short period event, why care how long it will last? the user maybe just toss it afterward. if me, if the pay for that event is very good, then go for brand name without 2nd thought, but if the budget is so so, then go no name brand, but if you can afford to buy double quantity cheapo is better, to anticipate for some lemon (dead) cells OOB.
(edit: sorry thought its international... OOB = out of the box)