I have a schumacker automatic battery charger and just got a new DieHard 71222 automatic charger from sears. $65 marked down to $40. The old one made me believe my bosch alternaters were lazy on topping the battery as it alway took half an hour for the green light on the charger to come on. On my US cars it would come on in 5 minutes or less. As a result I would throw on the charge bi-weekly.
On my new sears charger - the green light comes on usually less than 1 minute. Charging drops to zero or is auto stopped.
Newer is better?

I'm guessing your new charger is a "smart" or electronic charger which is the difference. Older chargers pretty much just charge one way, using one method (constant current, constant voltage, etc.); if "automatic" they charge until they see the current draw drop on the battery or the voltage at a certain level and then stop charging.

Newer "smart" chargers have multi stage charging which can use a variety of methods/strategies to charge a battery. Modes like bulk charge, top-off, maintain/float can all be integrated using charge methods that can vary between pulse charging, constant current, constant voltage, etc. They are indeed faster at getting a lead acid battery to full charge.

They're also better at stopping charge and switching to a float or maintain type of mode, which is probably what is happening in your case. I'm guessing the Schumacher is a standard older type charger and not a "SpeedCharge" model?

smaller batteries. As I recall even with the Schumacher when i put it on the 10amp setting the green light would come on right away.
The new charger seemed to have gone into a pulse mode on one battery. Green light would go on, then a pulse to 4 amps where the light went out, and repeat above. I'm becoming convinced that newer is better!