key fob problem on mercedes clk 240 convertible?

Out of the blue,my fob won't open on the central locking,nor open the boot. I pressed the lock button and it opened but set alarm off,then tried to close driver door but it would not close. Pulled internal handle up and button lifted and door closed pressing the lock button silenced alarm, key works in ignition. So I can drive but obviously can't carry on like this. Would this type of thing be simply a battery problem( bearing in mind the close lock works all the time)