Sorry, but the Spartan charge isn't that bad, if you keep getting caught you need to get better at avoiding it.
Be aware, watch your radar, most of the time you see it coming then it's time to react.
Thrust out of the way, either to the side or jumping back thrust.
Avoid it and you have the advantage.
If you don't avoid it make sure you get a melee in yourself as it does the same damage, if they are weak (shoot them as they sprint at you) you will get the kill, if they aren't weak its a matter of beating them to the no shield kill.
A charger cannot shoot on approach and their action is predictable, plus they can easily miss heir target... All this for standard melee damage.
I'm not a good player, but I eat chargers for breakfast man.