As it is, the hammer charge attack is one of most unrewarding, unforgiving, dangerous and pointless charge attacks in the game.
It pushes you right into the enemy, has to attack twice which means you're helpless for those 2 attacks, does damage equal to 1.5 of the normal hammer combo and the knockback isn't nearly good enough to justify using it for that. (As opposed to say leviathan.)
The only thing its good for is trolling AFK players by pushing them onto spikes.
I have a very simple suggestion to fix most of these issues.
Triple charge damage, reduce the number of attacks to 1, and give it knockback equal to that of leviathan.
There. Now the damage is worth it, it doesn't put you into nearly as much risk as before, and skillful attacks knock enemies away to prevent you from getting hurt.
I think the charge attack of the hammer was made to stand out of the troika line. it already has a very similar attack pattern.
I'd suggest the charge attack to work like this: you dash forward, then do a calibur spin with associated knockback. it would be a great tool to get in melee range faster than the normal attack.