Since we're talking batteries and big blocks, does anyobody know how much current the newer, reduction gear style starters draw, compared to the old style with the output gear directly attached to the rotor in the motor? I was shocked by how small my big block's starter motor is when I replaced it last year. It does not seem to draw my battery voltage down much when starting, but that might be a function of the big batteries.

If you are running a Volvo you need to use a cranking battery when the engine is running. The electrical systems are very picky on those engines. (this is also a requirement in the owners manual)

My information was that alternators do not power 100% at lower speeds.

I understand that Mutt, but not 100% of 55 amps is still a lot of amps, especially when compared to the 35amp alternators of years gone by. And I don't think 55 amp is the highest that boat are coming with now. As a matter of fact a it looks like all Mercruisers come with a 65amp alternator.

Good point.

Guess I should have checked there too!!

Just read the owners manual.

It states for the 8.1 Gi, to use a 12V with 650 CCA rating and 135 minute reserve capacity. It also states "CAUTION! Do not use a deep cycle battery as the starting battery."

It also says to not use deep cycle betteres on EFI engines. It says that it may cuase problems with EFI engines. Not sure why, but just telling you what is in the VP manual...

They are likely referring to deep cycle only, not the combo deep cycle/starting batteries. Both Four Winns boats I owned had Volvo EFI engines, and came from the factory with the combo batteries. Never any problems.

Deep cycle only batteries cannot easily deliver the amount of current that might be required to start the engine, which results in a lower voltage from the battery during start.

This likely messes with the engine's electronics..... just a thought.

Afterall, the attribute of a starting battery is the delivery of short-term, high-current energy, while a deep-cycle is the delivery of a long-term, low-current.

Right you are....

DING DING DING--- c'mon, someone else had to notice---

There is NO WAY that your #1 battery is going to start your engine, then within a few minutes, go "nothing...Totally dead", even if your alternator wasn't charging! (which is WAS, or the engine would've died if the battery WAS dead)

Something else is up. Not saying it's NOT the battery, it may have a broken post connection inside or some other anomoly, but batteries WILL NOT simply go totally dead 7 minutes after there was enough juice to crank your engine for several seconds.

That said, you should check all your cables, connections, and the battery switch itself. I'm almost willing to bet your battery is fine...

Speaking of alternators, many marine alternators need to be spun at subtantially more than idle speed before they start charging--watch your volt meter...

FR,

YOu may be right, but that is what happened. I'll try her again the next time it is warm enough to go digging around. It did take much longer than it usually does to fire up up when I first tried it.

Heading out to West Marine to get a new pair...of batteries that is.

How did it go?

I noticed in a earlier post it was mentioned to put in whatever the factory installed. I don't think all boats leave the factory with batteries installed, they may be leaving this to the dealer to take care of.

I am still running on my original batteries, Interstate brand, and will probably get one more year out of them. I charge them up for a night the first time I take the boat out. Just a long low amp charge.

I have had a time where the batteries spun the motor like a top but it would not start. Found out that the EFI will no fire the injectors unless voltage is at a certain amount while cranking. It is NOT much below a fully charged battery.

My batteries are used only for starting, I have no devices like a fridge to consider so I will probably go with two cranking batteries when I replace.

Good point.

Many times battery life is shortened when someone leaves something on and then someone does not either run the engine, or forgets to leave the shorepower cord plugged in when you are away, or unknowingly messes with your charger set-up.