How long will it take for a very dead iPhone 5 to charge?

Need to charge my iPhone 5 up, it's been dead for probably about 3 years sitting in the box. I have had it plugged in for about 35-40 minutes and it was showing no sign of life, totally black screen. I saw something online that said if I charge it for about 30 minutes and then hold the home and lock buttons... show more Need to charge my iPhone 5 up, it's been dead for probably about 3 years sitting in the box.

I have had it plugged in for about 35-40 minutes and it was showing no sign of life, totally black screen.

I saw something online that said if I charge it for about 30 minutes and then hold the home and lock buttons down at the same time it should re-boot.

I did that and it didn't re-boot, but it did flash up the battery image showing a very little bit of red at the bottom of the battery.

Does this just mean it needs longer to charge, or is it just totally dead and there's no hope?
Update: I decided to just leave it charging and after about an hour it buzzed to life!
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