Standard lead battery in place of AGM?
 

Sorry guys, didn't know where else to put this.

I've got a C300 right now that needs a new battery. The car belongs to a family friend who has gone back overseas, and I'm trying to get it into "sellable" condition.

I'm wondering if the original AGM battery can be replaced with a standard lead battery? From what I've been reading, it seems like there shouldn't be a problem, but I figure there's someone on here that knows much more than I do.

Can anyone offer some assistance?

By the way, what is that drainage tube on the side of the battery? Is it specific to AGM batteries? Sorry, I've never had a fancy car of my own!

Thanks in advance