Yes, I guess it could be the batteries but in my remote they have lasted for ages, I suppose it depends how much you use it.
If the the led stops flashing when you press the remote button then that says to me that its getting a signal from the remote, what happens if you press the buttons on the Coin Kit board ? do they work?.
If you have more than one remote, can you try another remote with the Coin Kit ?.
If you have another Coin Kit, can you try the offending remote with another board ?.