battery upgrade

Cruising these posts I see a couple of reccos for a battery and/or alternator upgrade.  As is, the amp I'm using only puts out 400w rms total, but I'm tossing around the idea of getting another to push my internal speakers.  At what point should I begin looking into an upgrade?  The numbers I've seen were 2400w & 1200w, so I'm curious as to what kind of power starts to put a noticable effect on the electrical system.

a good measure to find out the cuurent draw of the amp is power/volts .....so 400/13.8=28.9 so about 30 amps of the factory alterantor is gonna be required to push the system, so if your factory alternator is rated at 60 amps half is powering the system, if you were to get another 400wrms amp     800/13.8= 57.9 almost the amp capicity is used for the system...so upgrading the alt is always a good idea when getting high power systems....

I 2nd trusdamanr but there is no real way to tell how many amps the car alone (not including any aftermarket upgrades) at full load will draw with out testing it. If you go to an alternator shop they have a machine that will tell you how much of a load is on the charging system at any given time. But most of the time its just common sense  People don’t realize how much of a strain a small 400 or 500 watt system can put on the cars charging system not to mention their audio equipment. But I would defiantly get a high out put alternator if you add another amp.

Amen brother get that alt and a good batt to start. that is the heart of the elc system.Big Dave