Got a transponder/fob low battery warning message on the dash so swapped the key fob battery out. the battery is a single Cr2032, duracell ones are about £2 for 4!, dont pay over the odds a cheeky dealer on ebay are selling a single battery for £5 posted, and I notice they have sold 24 of them. needs a pound coin inserting in the corner gap left when you flip the key and a give the coin a firm twist. Its a bitch to prise apart so dont use a slimmer coin than a quid it may leave marks. The circuit board inside fell out of its own accord (nice!) and the old battery simply pushed out. Clipped the circuit board back into the bottom half of the fob after swapping the battery over but wouldn't say it was a tight fit, pushed the two halves of the fob together and hey presto, bike started and no dash warning. Have now stuck a spare CR 2032 battery under the rear seat just incase, could be 50p well spent.
Took mine to dealer and had the battery changed at a cost of £5 two weeks ago and the low key battery warning came on again today!!
...but do get a 'quality' brand (they definitely last longer;-) and do check the expiry date on the packaging before opening! More 'how to' photos (full size versions) here.
You may know this already but if your battery does go flat without enough warning for you to get it replaced, you can still use the key in "passive mode" even with a dead battery.
