I had that problem previously - But now they are an important part (tho I dont use loads of them) of my British armies.

I send them in the flanks of the enemy about 5 seconds before I send my inf in. I also keep them in a medium deep formation - not the thin formation they deploy on.

As soon as they hit the enemy I draw them out again - leaving much chaos and unformed ranks in the enemy - who usually then rout as my inf and/or cav charge in.
If they dont rout then now that they are engaed with my main battle line - I re-send the chariots in from behind - immediate rout - minimal losses. Its only if I leave the chariots in melee do I get huge losses (except ve cav - they do well in melee with them).