I guess good damage boost and 7-8 AP needed to throw one grenade will make the things more balanced.
Comparing grenades to other weapons (rocket launcher)
Rocket Launcher
7AP, 35-100 damage, 40 range, must reload
Always keep that in mind. Grenades have the advantage of not needing to reload, but at the very best you have 15range. A reduction of 25 range is hardly worth the lack of reloading.
But really: Do we need another weapon with the exact same role as rocket launchers? I keep hearing people complain about grenades being overpowered but i wonder how much of a bandwagon fear this has become. I've had 2 friends complain to me about how overpowered grenade builds are: Only to find out they've never actually fought against, or fought as a grenadier. Simply the idea of "2ap grenades" scares them, but forget various factors, such as 15m range.
If grenades really are overpowered its simply because it has the ability to keep people on the ground more easily than other weapons. If there is to be a nerf, then simply remove fast shot's effect on them, and boost the damage of grenades enough that the DPS stays the same. Don't turn it into a near copy of rockets though, theres a lack of variety of builds as it is now...