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. <BR> <BR>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.) <BR> <BR><a href="http://www.amazon.com/Battery-Marine-monitor-anti-theft-device/dp/B0015FXHM2/ref=sr_1_7?ie=UTF8&amp;s=sporting-goods&amp;qid=1241462078&amp;sr=8-7" target="_blank">http://www.amazon.com/Battery-Marine-monitor-anti-theft-device/dp/B0015FXHM2/ref=sr_1_7?ie=UTF8&amp;s=sporting-goods&amp;qid=1241462078&amp;sr=8-7</a>

you need a second battery if you have amps and ever plan to sit w/o motor on IMHO. If you never really sit ever for longer than 30 mins you would be fine with one battery but why gamble?

You own an 05 supra and your questioning spendig a measley $100 on a second battery? You have absolutely nothing to gain by not having a second battery...but you can potentially ruin your day on the water.

Like tony said, you need a second battery if you want to be sure that you can start your boat, and run accessories without the engine on. <BR>Then you need to isolate the two batteries so that one is dedicated to running the engine. <BR> <BR>(Message edited by rallyart on May 04, 2009)

The day you buy a boat!

^^^2nd that there's no reason to not have a second but the reasons for getting it are many.

Got it, people like having a 2nd battery. <IMG SRC="http://www.wakeworld.com/MB/Discus/clipart/happy.gif" ALT=":-)" BORDER=0> To be clear, I never questioned spending $100, the question was taking up more space in my already crowded dry storage area that's filling up with stereo related stuff. Anyway, I understand the value of a 2nd battery for helping prevent the battery from draining when the engine was off. My real question was, is there ever a point where one battery isn’t enough even when the engine is running? But, now that I think about it, I guess that’s more of an alternator question since the issue would be not being able to keep the battery charged as fast as it’s being drained. Hmm, I'm pretty sure I'm not near that limit, so I'll retract the question! Thanks for the replies.

Cheap insurance to ensure a day of fun vs. waiting for a tow.

It's either a spare battery or a jumpstarter box you'll have to carry. Might as well have a battery.

A related question. <BR> <BR>If I want to run 2 isolated batteries. What type of switch do you need to toggle between the 2? <BR> <BR>For example if I sit and listen to tunes for 1/2 hour then I want to switch between the batteries so when i'm running again it recharges the drained one. <BR> <BR>I'm sure this has been discussed before but I get a bit confused when the battery talk starts

What you need is a switch such as Perko's 1/2/BOTH/OFF switch. You can also go with an automatic Isolator or an ACR (auto combining relay) such as from Sure Power or Blue Sea. No need to mess with a switch for automatic charging with engine running and isolation when engine off. I would recommend adding a switch anyway, this will allow you to use the house bank to start engine if starting battery takes a dump.