I would never reccomend a caffeine or stimulant overdose as I've survived one and it was horrible, but to answer your question:
The median LD50 for caffiene is 150-200mg per kg. Let's assume it's 200mg/kg.
One can of Regular 5-H energy has 200mg of caffiene. Doing simple maths, assuming your body weight is 70kg, you would need 70 cans of 5H energy to have a 50% chance of death. And it would be a terrible death at that.
I must say that this is assuming you're healthy with no heart issues, and as is with almost every substance, the lethal dose may slightly vary from person to persons. Take care.