Bare with me on this thread as it may get long. I have a 2000 260 Velocity in 2002 I upgraded the stereo (Sony), speakers (Boss) and added an 600w amp (Bazzoka) and a second battery. I ran the battery switch on "all" al of the time and turned it to "off" when not in use. I never ever had the battery drain to the point I couldn't start the boat.

This past winter I added a 10" sub (Kenwood) with a 700w amp (Bazooka). I have been out 3 times this year and have had starting troubles everytime. First time i noticed the Volt gauge was only reading around 12 while at idol or running well after the 2nd day I had to jump the battery to get it back to the dock. The next day I went to have the alternator checked and it checked good. So next weekend I disconnected the new amp and ran the battery switch on 1 then 2 and noticed that the 2 side (Cranking battery) was not charging as well but had no starting issues. Replaced the cranking battery and this weekend I rewired the new amp with #8 wire to the #1 side of the switch (house battery). Went out this past weekend and boat wouldn't start unless I was on "all"!

What am I missing here? I have had no troubles in 8 years and the only thing I did was add a sub and amp and now all kinds of battery issues.

If someone has any ideas I would greatly appricate it.

Is at least one battery a DEEP CYCLE? If not, you're definitely going to need at least one deep cycle battery to run that stereo. I went through the same thing last year, and couldn't figure out why my batts were draining all the time. I also have a 700w amp running 2 10" and 3 sets of components.

Yes one is a deep cell. I put it on the battery tender yesterday around 11am and it taken until sometime this morning to get to an 80 percent charge, which to me seems like a the battery should have had that much drain in only one day on the water. I didn't even play the stereo this weekend while out. Maybe the deep cell is going bad?

I'm not sure why you are confused.
You say that your previous configuration did not leave you stranded, so you can't see why it's happening now that you;ve more than doubled the current draw on your bank of batteries. If you plan to listen to that system at the volumes you're listening, you need more batteries. End of confusion.

Each battery will deliver 80-100 amp-hrs of power. Combined, let's say 170 amp-hrs.

This means 17 amps for 10 hours will drain them.

A stereo amp is generally linear regarding its current draw. At low volumes, it will draw low current, and at high volumes it will draw high current.

An amplifier cranked all the way up delivering 600RMS watts of music power will be drawing 660 watts of juice from your batteries (at 90% efficiency). At 12 volts, this is 55 amps.

An amplifier cranked all the way up delivering 700RMS watts of music power will be drawing 770 watts of juice from your batteries (at 90% efficiency). At 12 volts, this is 64 amps.

With everything cranked up, you are drawing 119 amps from your batteries, which will suck your batteries dry in 1.5 hours.

Clearly, listening at lower volumes will draw less power and will extend the power reserves of your batteries, but when we look at the worst case scenario, if you have three chicks on a stripper pole on the front of your boat and you're blasting at the limits of your amplifiers, there will be nothing but silence before the second hour arrives and there will be no juice left over to start your engine(s) to get you back to the marine for more Astroglide.

There's several options here.
Drop in a third battery to use as your starting battery. If you are worried about weight (speed penalty) or have space constraints, then you can drop in a smaller, lighter battery. It's going to have to start your motor and that's it. Doesn't have to be a big Group 31 size. You can probably get away with one of those larger $19 yard tractor batteries if the truth is known.

For wiring it up, you can keep your same battery switch. Run the small battery on one circuit, and strap both "house" batteries together on the other circuit. When you aren't running the engine, keep the switch on the house cells. That way when you're dead, swap to your start batt. Fire it up, and go get your Astroglide.

Now, regarding charging by alternator, it is BEST to use a battery isolator to charge banks independently. It is NOT required, but it keeps the starting battery from getting punched in the gut when (after you start the motor) you swap the switch back to ALL. That way, you fire up your motor on the start battery and drive off. While you drive, the house bank is being charged by the alternator and everything else is "running" off of the start battery. This preserves the "health" of your starter battery, since it doesn't have to do a high amp "refill" into two big fully dead house batteries.

MC

mcollinstn, thanks for the advice. My confusion really came into play this weekend when I only turned the stereo on for less than 10 minutes, I had nothing on while on the hook for about 2 hours, when I went to start it I had to but the switch on "all". The amps are wired to the head unit so with the stereo off the amps are off.

Niether battery should have be drained to the point either of them couldn't start the motor?

I personally don't think that your issue is with the power that you've added to the stereo, I think you have a bad battery.

I would try taking the deep cycle out of the boat and putting it on the charger. See what kind of volts you get out of it after it's been on a charge for a while. After that disconnect the battery, but leave it on a bench or somewhere that shouldn't cause a drain (don't leave it on the ground). Test the battery after a day or two of sitting and see if its dropped.

I'm going through somewhat of the same issue right now. A bad battery can make a voltage gauge read improperly if its eating volts, but I've had alternators that were bad read good while they were being tested.

Thanks wjb21ndtown, was thinking along the same lines as you! I will try that tonight.