I have something to add in regards to the phone dying. When you are in an area where your phone is constantly trying to search for signal it drains the battery quicker than even you using it to talk or text on. If it were to go dead then no amount of sending messages to it will help you find it, you better hope you can find it on your own. Now the bad thing, what happens if you walked outside with both your phone and your ipod, let's say to text and listen to your ipod while doing it. Let's say you put your phone in your pocket and somehow it falls out. Your dad is in bed, and you don't have access to his phone. How would you find your phone? You couldn't use the ipod to text it because it would have to be close to the wifi signal source. You can't use the landline to call it because you would need to be outside to find it. So your only option is to retrace where you walked the night before when daylight comes. So, if your phone is dead, you were suppose to be at your friend's house at 6:30 am, you dropped your phone somewhere outside, what would you do? Would you grab your bag(that you may not have unpacked due to getting in late-ish the night before) head out and look for your phone along the way, IF you were too impatient to wait for your dad to get back and give you a lift? We don't really know what Dylan may have done after Mark went to bed that night either.
Mark said when he went to bed Dylan was still texting right? Some people don't look at a clock when they go to bed, they just go, especially if they are tired. They can guesstimate the time they went to bed, maybe around 10 oclock. If Dylan was still texting when Mark went to bed, that would seem to imply Mark went to bed earlier than what he said, or you can choose to believe it's because he lied about what time he went to bed.
Then again, we know LE has verified that Dylan made it to the house. The phone pings and return texts would NOT necessarily show that Dylan made it to the house that night. However, what if there was a text from another friend after Mark went to bed where one said they were going to stop by, meet outside. Something like that, and that friend saw Dylan at the house? Then Mark claims to have seen him the next morning. Perhaps the friend was able to verify that Mark was in bed at the time he stopped by? We really don't know how they verified he was arrived at the house, just that they did. Would they take phone pings and texts as absolute proof?