Hi, in this case, no there is nothing that will happen to the GPS to let you know its charging unfortunately.
But...you should not try to turn it on until about 4 hours have past.
If you try it then, and it doesn't turn on, you will need a new battery in the Magellan.
Its easy to replace and I will help you with that as well once you have the new battery ;-)
The best place to get a new battery is : http://magellan.factoryoutletstore.com/cat/1547/Magellan-RoadMate-Series-GPS.html?cid=1681&chid=2
But I would call them to place that order if you need it:
In any case, I will stick with you until this is complete.
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