On the "message sending light" I've learned best to just set the thing down - I usually set it on the fire ring - and let it time out - about an hour.  Unless something blinks red, I know it completed the sending process and is indeed "sent".  I caused some concern first trip thinking it was a message sent indicator and turned off the Spot before it had actually been sent.

Even timing out with Spot 2 - I've made several week long trips - a year apart - on same batteries.