Well after well over 4 years sterling service my 550 just gave up the ghost and refused to switch on 
Tried taking out the battery, pressing the on button at the same time as the + button but no good. Left it to charge on the mains charger overnight and still no good
Sods law as I only updated the maps a couple of week ago
Phoned Garmin and they will repair or replace it for £111 which is I guess better than spending £400 on a new one.
So posted it off this morning and will see how long it takes to get back to me. They have at least promised that I can transfer my lifetime map updates to the new unit if it is replaced
Will see how long it takes to get back to me.

Tried taking out the battery, pressing the on button at the same time as the + button but no good. Left it to charge on the mains charger overnight and still no good
Sods law as I only updated the maps a couple of week ago

Phoned Garmin and they will repair or replace it for £111 which is I guess better than spending £400 on a new one.
So posted it off this morning and will see how long it takes to get back to me. They have at least promised that I can transfer my lifetime map updates to the new unit if it is replaced
Will see how long it takes to get back to me.