charging a battery?Late for work!

I have an old charger 6A/12V is it ok to hook up to battery directly w/out disconnecting battery guage on charger reads 3A. Is it also ok to try to start w/disconnecting charger or do I need to connect charger via ground as in jumping methods?

I'm late for work.

Well it started, no smoke or adverse effects still no C.E.L. (RENIX joke)
Had it hooked up directly to batt. posts and disconnected after it seemed to have enough power to turn engine over

If anyone has any info pro or con about in car charging please post up what you kno, also when I did pull battery out months ago and overnight charge is the charger supposed to hum really loud?

I When I kill my bat I just hook it up to my charger set to "55A Start" and start it then disco the charger. A lot like jumping