Wildfire

Working on the Magnum and am confused about the batteries.

Single engine, one alternator
Two batteries

Ground 1 connected to block near starter
Positive 1 connected to starter

Ground 2 connected to block near water pump
Positive 2 connected to positive 1 (Is this normal????)

Alternator output wired to amp guage that does not move, maybe a bad gauge or maybe a bad alternator. Who knows? How do I find out?

There is no 1-2-off-both switch (or any other switch either)
I have not found an isolator

How many volts do I have?
Is this normal?
What all is wrong with this (if anything)?

The boat cranks and starts properly - have not tested for long periods of time though.

I am going near a West Marine tomorrow, so quick responses are most appreciated.

The thing that makes me mad is that most of my tools are in storage and are DIFFICULT to get to.

Cord

If the batteries are next to each other you can go negative-negative-block and positive-switch, postive-switch with the single switch going to the starter. If they are apart you can go negative-block, negative-block and positive-switch-starter, positive-switch-starter.

You will have 24volts if it goes negative-positive-block and positive-negative-starter

...I think.

If you have a clock, I'd also advise wiring that off the hot side of the battery switch. That way you don't have to always reset the clock. Just disconnect the battery over winter to prevent a excessive drain.

SFOcean

You have 12 volts with twice the amperage as both batteries are connected together.
It is a good idea to isolate them by adding a battery switch for two batteries and run one one battery at a time, that way you have a good battery if you run one down.
Use Cord's connection method - negative-negative-block and positive-switch, postive-switch with the single switched wire going to the starter.

Wildfire

OK, so I have twice the amperage. That is a good thing.

How about this? Any problem doing it with a single 1-2-both-off? Other than me forgetting to use the switch?

Cord

Unless you are running a cruiser, I'd drop the isolator. That device is meant to automatically separate one battery which is reserved for starting. If I am correct, that battery will not be charged-hense the battery charger. That charger will run off line voltage which means that you'll need either a genset or some other 120v source. This would be a acceptable setup if you have more than 2 batteries or have dedicated deep cycle batteries.

Once you take out the charger and isolator, you basically have the layout that we've been describing. I'd recommend running a dual purpose deep cycle/starting battery. Yea the battery costs more and cant do either job as well as a dedicated battery, but they are much more flexible and versatile.

Wildfire

Here's what I ended up with:

A 1-both-2-off lockable switch with the alternator field disconnect.

Battery combiner. This thing is supposed to allow both batteries to charge at the same time, without letting battery 1 draw down battery 2 if battery 1 goes bad. If it doesn't work, then I fell for West Marine's advertising "advice".

One more positive cable.

I think the charger is there just to keep the batteries topped off. It is a low, low amperage maintenance type. Plugging the boat in should always keep the batteries ready to go - theoretically.\

Thanks for the advice, you guys really helped me out especially since my boat wiring book is in storage, right next to my tools.