Have aquired TomTomTruck 7150 which was not working, when plugged into charger there was no light so assumed not charging. I replaced battery and unit worked but will not charge, orange light flashes and eventually battery expired so obviously not charging. Have tried various tested chargers and result is same so not charger fault. Don't know what orange flashing light signifies, any ideas?

Most likely hardware failur due to the faulty battery.
The charging circuit failed.
You can search Google for the problem and check if the pics from other devices match your circuit board.
Often it is just an electronic fuse or tiny resistor that is damaged.

Ok thanks for that Downunder, I recharged the battery on another unit and refitted it to the 7150 and it works very well but obviously it's no use if it can't charge under it's own steam. Thanks again.