EV Mode in the 2010 Prius...how far?

When putting the the 2010 Prius in EV Mode, is there a risk of damaging the battery if you drive too far, according to Page 169 of the owner's manual the computer simply takes the vehicle out of EV Mode when it see's the battery has gotten to low? Am I correct in assuming this will automatically prevent any damage to the battery from let's say a 3 mile EV run. I was taking a drive up along the Delaware river, upon approaching the the river there is a steep down hill of about a mile. Breaking all the way down, at the bottom of the hill the battery charge indicator was all the way up. At the stop sign to turn up along the river road I put the 2010 Prius into EV mode, went all the way through the town of New Hope in EV and proceeded up along the river for about 3 miles (Well that is distance in EV mode, but there was a fair amount of coasting.) I probably could have gone farther, but I eventually had to increase speed above 25mph in a 35mph zone when a car came up behind me and I did not want to be a PIA for them. This was around 1 AM. I was pretty impressed, thinking EV mode would only be good for a half mile.

Is this a practice I should really avoid?