Ok, I did a quick search and saw lots of threads on amps and batteries, but not one that said how you know when you are drawing enough juice that you need to add a 2nd battery. My current setup has a 60X4 channel amp plus 50x2 from the head unit running all the cabin speakers and a 200W Inifinity BassLink subwoofer. I'm about to add a Kicker ZX450.2 and KMT6 Tower speakers, so that's another 300W (150x2) which takes my total from 540W to 840W. So, I guess that means maxxed out it's drawing ~70Amps(?) Am I going to need a 2nd battery for this setup? I'm mostly concerned about what's needed to provide enough juice when the engine is running as I don't tend to sit for long periods of time with the boat off and the stereo running, but I would like to be able to do that for at least 20 minutes or so (at lower volumes) without worrying about it completely draining the battery.
I'd rather avoid a 2nd battery if I can just to avoid using up any more space in my dry storage, but I'll add it if needed. On that note, has anyone tried the battery brain? At $100, not much financial savings over having a 2nd battery, but looks like another good option for piece of mind (and doesn't take up precious boat real estate.)
http://www.amazon.com/Battery-Marine-monitor-anti-theft-device/dp/B0015FXHM2/ref=sr_1_7?ie=UTF8&s=sporting-goods&qid=1241462078&sr=8-7