A cellephonic mystery

When the SRE came home from office on Saturday evening (yes, he works most Saturdays), he was distraught. His cellphone was completely and utterly dead- not a glimmer, not a twinkle, not a beep out of it. We put in to charge, hoping that it would revive once it had some power in it. But it remained completely and utterly dead. Not only was he phoneless, he has huge amounts of important data on that phone, so he was understandably upset. On Sunday morning I called his secretary to get the number of the person who supplies phones to the office. The gentleman was told all the gory details, and said he would send someone to the office first thing on Monday morning to collect the phone, and try and retrieve all possible data. As instructed, I put the phone in the SRE's laptop bag, so that it would get to the office.

We had a nice and peaceful weekend, without the phone making its presence felt every few minutes.

I needed to speak to the SRE a few minutes ago, so I called him on his direct landline number. After telling him what I had to, I asked him if the phone chappie had collected the phone. He had come to collect it, but it turned out that after being comatose for over thirty six hours, the phone was alive and well again, and was apparently showing that it was 80% charged!

Now how did this happen????? Any ideas????