Mine was getting a little slow response wise so I popped it open to clean & replace batteries.Thing is this remote has 2 batteries, I cannot remember how they came out positive sign facing up on both?There is nothing separating the batteries they are really just sitting on top of one another lol!

 

Exam the area where the batteries sit. One side will be a plate area only and the other will have a piece that is somewhat of a spring like affair. The spring side is the negative.
Generally the batteries will be both positives facing the fob with the negative sides facing the cover. They stack one on the other.
It really doesn't matter if you get them backwards the fob won't work. Just turn them around if it doesn't work.
I haven't changed batteries in quite awhile but went thru the same as you except mine fell out without any hint as to how they were installed.
Just remember the positives both face the same way.

 

Also, while you got it open push the board out of the case and off the rubber.
That side of mine was full of goop.
Wash plastic and rubber with soap and water and cleaned board with electrical contact cleaner. Now works like a champ.

 

This is what my X308 Fob looks like...

 

Awesome!

 

It is stupid that the fob uses 2 very thin batteries. I actually replaced mine with a single thicker battery (2032). That one battery is the thickness of the two original batteries together. I havent had any issues. Every other fob I have owned has only had one battery so I dont see why these have 2.

 

Yeah it is odd, my last one was a 2001 as I remember it only had one, this is a 2000 & has 2.