It once so happened with me that I was travelling from Mumbai to Falna equiped with SMS from IRCTC and ID proof. We boarded the train at 3:00 pm and we waited for TTE to show up but no one turned up to check the tickets.
I the mean time I kept on using my phone for surfing etc. and my battery almost died down by the time it was 10:00 pm. At that point my wife suggested to switch off the phone and we went preparing to sleep. At around 10:30 pm the TTE came, he checked the ID and asked for ticket.
I...
more... explained that my phone is off since battery has died down. However, he insisted for SMS or ticket. I turn on my phone. He waited patiently. Luckily the phone had just the right amount of power and I was able to show the SMS. The phone then turn off. He later explained that he need to check the PNR.
Since then my family always insist me to carry print of tickets.