Your 8.1 should be 650 cranking Amps and 135 reserve capacity.

Most say to not use a deep cycle as a starting battery.

SB, where do you get that info? I have been wondering if my 350 mag / B3 has the right battery, do you know what I should have?

I'm with Waltermutt. If you can handle the upfront cost, Optimas are the best.

If you don't get those and you are wired correctly for it, I get one starting battery and one deep cycle battery. I have the Optima blacktop as a starter and blue top as a house battery.

D-Rod, why have 2 starting batteries? A starting battery will have a very short life if you totally cycle it i.e. you run it dead by using it to power your stereo system with the engine off. On the other hand, that is exactly what deep cycle batteries are made to do.

Can't start a big-block of a deep cycle either. So much for the "rotating" the battery method. Worthless to have a deep-cycle and forget to switch to it and kill your starting battery.

Unless he has a twin sub radio he's playing for a very long period of time, a starting battery should run the standard stereo for a while without problems.

D

I have always bought the combo deep cycle/starting batteries.

I do not want to give away some resources, sorry. I often walk a fine line on some stuff.

Some folks recommendations are not as detailed/not as specific, and that is about as high a spec as I know.

Note, many cut back with certain changes in specs, like a 3.0 or a carb engine.

Fi system needs can often be the reason that she will not start.

Al,

Do you have a link to some of these?

I'm no battery specialist, but like Al, I am migrating toward Deep Cycle Batteries.

I guess the knock on them as 'starting' batteries, is the concern that they cannot produce enough Peak cranking power over a few seconds (3-5?).

I'm not sure that is true in all cases anymore. My Exide Orbital puts out 950A Cranking Amps at 32 Degrees, 1100 Max Amps at 5 Secs.

(But is printed on the labeled as a Marine Deep Cycle & Starting battery)

That's not a true deep-cycle Ken. It's one of the hybrids Al and others have talked about.

A true deep cycle battery is damaged if too much current (like 100 amps) is drawn.

http://www.interstatebatteries.com/content/product_info/marine_f.asp?js=1

First category - Deep Cycle/Cranking

In my opinion, the big benefit to Deep Cycles come in not while the engine is off and you have the radio / blender / lights / bugzapper / spotlight etc going. But at low engine speeds, you alternator doesn't always fully support your full power usage. Long idle times like a no wake can draw down a battery, from what I understand.

WM, I not sure about that....

Once the engine is started/running, the alternator powers all the systems' electrical needs AND charges the battery(ies) (even at idle).

In fact, an engine can run without a battery, once started. (at least in the old days). Once the engine is running, the battery is basically only needed to complete the electrical circuit.

(That's my shade tree mechanic and many failed batteries experience...in autos...)

Maybe on a cruiser or something but I can't for the life of me think of what could draw so much power on a bowrider/cuddy.

Exactly, and with todays 55amp or more alternators, I wouldn't dee how it couldn't provide enough juice at idle to power everything.

But for me, if in the future I anchor or raft up and have a lot of load on my electrical system, my "house" battery will be a deep cycle. And my starting battery will be a starting battery. I currently have two starting batteries, but I really don't need two. And I don't draw harldy any power when rafting out. Just a cigarette lighter fan.

Well, I told you .

We had an usually warm day today in the DFW area. Around 70+ degrees and virtually no wind, so we fired up the ole 240. Well, sort of. I switched to the 1 battery (as both are cranking batteries) and started her up. Took about 4 seconds and she fired up. I let it idle for about 7 minutes just to let her run since its been awhile since I had her out. I turned it off while I waited for my wife and my daughter and her friend to arrive at the slip ( I always have to go first to get it ready...heaven forbid they would have to help ) I tried to fire it back up on the #1 battery and yes, you guessed it .....nothing. Totally dead.

So, I switched to number 2 and she fired right up. We cruised around for about 45 minutes before stopping for a late lunch at the marina bar/grill. After about 40 minutes I went back out, worrying I was going to be stuck, but she fired right up the first time...WHEW!!

So, I guess I really do have to buy a couple of new batteries. I think I'll wait until Spring is a little closer, as it will not be getting much use until February is out of the way.


Thanks for all the good stuff here.