My 2010 galaxy keep showing key battery low ,but I’ve changed battery in both fobs but the message keeps occurring , any ideas , 

What batteries are you using? It can say this with cheap/old batteries sometimes.

A decent brand like panasonic, duracell, etc can sort it.

Also make sure the battery contacts are clean.

Yep, Poundland batteries are no good

Batteries are Phillips & Duracell but still comes up with the warning message. 

Standing outside the vehicle, use one of the remotes and "Lock" & "UnLock" the doors 3 times in 10 seconds.

I’m not saying they are fake batteries but fakes do exist so where you buy branded batteries from is important . I kept having problems on my wife’s mazda2 until I bought some genuine duracell

For batteries, the absolute 1st point of call is to test them on a multimeter to see what voltage they are kicking out. When new, it should be 3.3v, anything less than 3v will give issues. Once you know the battery is good, then you can go down other routes to fix, no point wasting time if the battery (no matter what brand) isn't up to strength...