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why 2 batteries on boat?
On 4 Jan 2004 07:36:04 -0800, (mark s) wrote:
I recently purchased a new (used) boat. It has a 350 merc and uses 2
batteries.
I think 1 is a starting battery and the other is a deep cycle w/
cranking amps. There is a switch for the batteries to select #1, #2,
or both. No manual.
I am not familiar with this setup.
1 - why is this system utilized (why not just 1 battery?) and what is
the proper operation of this system?
2 - should I always have it switched to "both" so both batteries get
charged when running? what is the preferred switch scenario?
3- which battery is better to run the electronics to? (I imagine the
deep cycle.)
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The answer(s) should certainly be in the FAQ file if we only had one.
Here's the short and simple version:
The second battery is there primarily as a spare in case the first one
gets run down too far to start the engine.
There are exceptions to everything but as a general rule you should
NEVER switch batteries with the engine running. This can lead to
instant alternator failure under some conditions.
If you need battery 2 to start the engine, set the switch to #2 and
leave it there until the engine is warmed up and easy to start. Then,
stop the engine, switch to BOTH and restart. It's a good idea to put
battery 1 on a charger when you return to make sure it's topped off
properly.
My personal preference is for both batteries to be marine deep cycle
although some will disagree.
I occassionally start the engine with the switch in the BOTH position
to ensure that battery 2 stays charged. If you do this, you should
immediately switch back to battery 1 after you stop the engine.
Nothing except the primary bilge pump should be wired directly to a
battery. Everything else, including electronics, should connect
through the battery switch. One good reason for this is to ensure
that when you turn off the battery switch, EVERYTHING goes off.
Otherwise you risk leaving something on accidently which drains (and
ruins) your batteries.
That's the short and simple version. There are gadgets available to
automate charging of the #2 battery but that leads to a lengthy
discussion of pros, cons and risks. In any case it's a good idea to
have an accurate voltmeter and/or a low voltage alarm warning.
Using the strategy outlined above, battery 1 will get most of the
heavy usage and will need to be replaced more frequently than #2. My
suggestion would be to replace it at the first sign that it's no
longer holding a charge as long as it used to. In an ideal world you
should never use the #2 batt for anything but an emergency. If you
routinely discharge #1 to the point where it will not start the
engine, you will experience very short battery life. The best
solution is to get a bigger #1 battery with more capacity.
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