No, unfortunately these newer units don't have lights to indicate charge level.
Guess we need to see what is in your TomTom system cache, if anything. Click on the double red hands in the systray and select "Settings". Click on "Cache". Is the cache for large items selected? If so, do you know if your PC is configured to show hidden files and folders? If not, let me know, along with what OS you are running. On an XP machine, for example, you would find the TomTom cache here:
C:\Documents and Settings\Chris Anderson\Local Settings\Application Data\TomTom\HOME3\cache
We need to check to see if there's something there of an appropriate size to be a map and whether it is intact on your PC or not - I can't tell if the failure was the download or the transfer to your unit yet.
As I asked previously, "Have you tried reconnecting your 1535 to your PC to see if the update progresses further?" If the map download failed, MyTomTom should pick right up where it left off. What does the web page say when you connect your unit?