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Cruisingdad 11-27-2006 05:36 PM

Start Battery
After reading a couple of books (Nigel Calder especially), I wonder if the argument could be made to make your starting battery a true "starting" battery. Given the short use and high amps, wouldn't the thin-plated batteries be a better battery than more traditional deep cycle?

I am not saying you cannot use one for another, but the thin plates on a true start battery and quick surface charge (not to mention a lot lower cost), might make a true start battery a better option.


FrankLanger 11-27-2006 06:16 PM

I have two group 27 gel cell batteries in parallel for the house battery and a wet cell, no maintenance starting battery to start the diesel motor. I think this makes sense, except that in charging them both, it may be causing some issues, though I have the charger/inverter set for the more sensitive gel cell batteries and don't use the equalizing function (posted this on another thread on this topic.).
I think your basic premise of using a starting battery is sound.

hellosailor 11-27-2006 06:45 PM

Dad, a lot of boats now use exactly that. One cheap and small starting battery for starting, and one larger battery/bank for house use. If you match the starter current draw to what a deep cycle battery can supply as a surge load (i.e. starter load) then you can certainly use deep cycle for both, but the new logic seems to be reserving that special dedicated starter battery JUST for starting, and that also makes sure it is available when you need it. And, that it is cheap and easy to replace.

Faster 11-27-2006 06:47 PM

We have a similar setup - 400Ah in deep cycle and a standard high-cranking amp starting battery. Keep them separated, monitor the charge states individually - works great for us.
We never put house loads on the engine battery.

btrayfors 11-27-2006 07:09 PM

Indeed, keeping a separate REAL starting battery is the preferred way to go these days.

Re: charging, one of the simplest and most effective ways to keep both the starting battery and the house battery bank charged is to connect all charging sources to the HOUSE batteries, and to use a simple device which senses a charging load on the house batteries and diverts a bit of it to keep the starting battery topped off.

I've used such a device for several years with great success. Mine is a Xantrex EchoCharger which puts up to 15A into the starting battery whenever it senses at least 12.9 VDC or so on the house batteries. It is cheap, simple, and maintenance free. There are other manufacturers who make such devices as well.


gc1111 11-27-2006 08:22 PM

I went a step further and put in a second alternator, a simple automobile type that is old enough that it has a separate regulator, but if I were doing it now I would get one with a built-in regulator.

I highly recommend this approach - I have used the redundancy several times.

longwaterline 11-28-2006 10:51 AM

I agree the best bet is a separate starting battery dedicated to that one function. On Wave Dancer I have a separate G24 starting battery and two
G27 house batteries wired in parallel. Also have space for a third house G27 if I need the extra amp hours. The charging systems either shore power or engine based keeps the system topped off nicely. This the classic way to go although you see all kinds of arrangements and views out there on this.

Cruisingdad 11-28-2006 11:10 AM

I think maybe my thread was missunderstood, let me explain:

First, for those of you that may have read my threads in the past, I am a VERY STRONG ADVOCATE for a seperate, independant, out of the loop, starting battery. Period. If I am not mistaken, to meet ABYC, you MUST have it seperate. I think many manufacturers get around this by putting in a 1/2/both switch so that in theory one battery is a starter... whatever. Terrible setup. Terrible. And for those of you that are still doing what I did for many, many years (like switching your batts between 1 & 2 on even/odd days), you better read a few books about electricity. You exponentially (not linear) reduce the life of both batteries. Very bad idea. Go read Nigel Calders Boatowners Mechanical & ELectrical Manual, talk to a battery manufacturer, or any electrical engineer. Parallel is much, much better and will vastly extend the life of boat batteries. I guess the exception is if you do not have a starter battery... but I don't think I need to cover that ground again.

Now, my statment:

Deep cycle cells are built with heavier, thicker plates versus a typical start battery is built with a typical thin plate. We tend to (as cruisers) associate a thin plated battery as bad and a thick plated battery as good. This may not be the case at all. When you start your engines, there is a huge, but short (hopefully), amp draw which pulls the juice off the surface of the plates... but that is it. This can then be easily replenished with a quick charge. A deep cycle battery would also pull the surface charge off but then get deeper into the plate, requiring what we often assocaite with as needing a multi-state charge to replenish the "interior" of the battery, not just the surface.

Yes, you can use a deep cycle... but the questions is, perhaps it really is not the best battery for that purpose (not to mention the cost)? Could the argument be made then, to use a true, NON deep cycle battery?? I would say it could. My logic off anywhere here?

dave.verry 11-28-2006 12:24 PM


Exactly right. The thin plates are there to allow the manufacturer to stack more of them in the space. More plates = more surface area = more possible current (starting current or CCA, cold cranking amps) Starting batteries are optimized for short, high current discharges followed by short (relative) high current charges, as you would find starting an engine.

Can you use a deep discharge, yes, should you, probably not. If sufficient current is not available to the starter then the starter speed will be reduced causing harder starting. Compounding this the voltage available to the engine will also be less and if itís a gasoline engine, harder starting (Iím not sure about diesels, never having worked on one).

Using a deep cycle battery for starting is as wrong as using starting batteries in your house bank.

thegolux 11-28-2006 01:17 PM

This thread has gotten me thinking, which is a dangerous thing. If it is beneficial to use a high CCA, thin plate battery for starting, would it make any sense to use the same kind of battery as a dedicated battery for a bow thruster? You would use it infrequently, relatively speaking, and if it was mounted near the bow, you would reduce the length of heavy wire required. Since I know almost nothing about bow thrusters, I may be asking a silly question, and if so, I apologize.

I was looking at wire size tables and to carry 500+ Amps (746 hp/amp x 9 hp/12v = 559 A), it would take 4/0 wire (or better, depending on length of run and tolerable voltage drop).

Just asking.

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