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GarrettK 09-16-2004 12:45 PM

Starting Battery vs. House Battery
I''ve done a bit of research and am still a bit confused on this.

My plan is to have a 3 battery system in my new to me Pearson Wanderer. It will consist of 2 banks, the first being a single battery for the motor, and a two battery bank (house batteries) for all other electronics.

The house batteries will be deep cycle batteries. The question revolves around the selection of the motor battery. From my research, I''m better off having 3 identical batteries (from a charging aspect), but for a starting aspect, I don''t want this to be a deep cycle battery (or am I wrong)?

Basically, is there a problem using a deep cycle battery as a starter battery for the motor? If it matters, the motor is a 25 hp Universal diesal.

The electrical system on this boat is a nightmare and I''m basically going to gut it and start over, but want to get it right the first time.

I''m currently working my way through Nigel''s book on electrical systems, but have this one question (for now).


boatbum 09-16-2004 01:28 PM

Starting Battery vs. House Battery
Good plan on the battery set up, however a slight improvment could be made.
First, the starting battery should be just that, a Group 24 or 27 will be fine for the Universal 25, had one on my last boat. If you can, use 6v golf cart batteries for the house system Trojan T-105''s, you will need 4. Each bank is connected in series to have 2 banks of 12v capable of very deep discharges and multiple ones. Should get 5 years from the set up. Next, the 35amp alternator on the Universal is too small to charge these batteries fully or any other mix you might come up with. I used a new 105AH alternator and a smart regulator. That is the max you can turn with a single pulley set up, and at that you need to use a Gates Brand belt. When the altrnator kicks in, you''ll take about 300 rpm off the cruise. It''s noticable. This set up served me well running everything on the boat, refer, etc. Good luck.

RichardElliott 09-19-2004 08:19 AM

Starting Battery vs. House Battery
I''ve been very happy with the Optima AGM deep cycle batteries for both uses with a Universal 25hp diesel. They do not require water top off.

jbanta 09-19-2004 12:52 PM

Starting Battery vs. House Battery
They don''t require water ever thats true but like anything else it''s a trade off they don''t have near the storage capacity of a flood battery. Each must decied, based on thier boat power needs just what type battery bank is the best for thier curcumstances

Jeff_H 09-19-2004 06:28 PM

Starting Battery vs. House Battery
Jim, I believe that AGMs have a much greater storage capacity and are longer lived than a flooded battery but they are more expensive and require proper charging and voltage control.


mmccoy 09-20-2004 03:55 AM

Starting Battery vs. House Battery
Garrett asks a very good question.

I agree Group 24/27 batts for starting & T-105''s for house would be a good choice and is exactly the setup I''ll use to replace my current 2 banks of group 27''s.

But what about the different charging profiles/characteristics of the the two different types of batteries? Would a multi-stage smart charger (i.e. Xantrex Trace 20, etc.) handle charging the two different batteries appropriately? Or would you need 2 independent chargers to charge the different batteries properly?

boatbum 09-20-2004 04:41 AM

Starting Battery vs. House Battery
I have the same set-up including the Xantrex. The charger is also smart enough to tell when one bank is up and then divert extra amps to the lower banks until all are charged. I''ve had this set-up for two years and it is great.

GarrettK 09-20-2004 08:12 AM

Starting Battery vs. House Battery

Thanks for the reply. That was going to be my next question, but mmcoy beat me to it.

So if I understand this correctly, I want to use a 24/27 size/style battery for starting (as bank 1) and then 2 105''s for my house battery (bank 2) and a 3-stage charger will adequately charge the banks even if they are different types.

I''m sure I''ll come up with more questions as I start this project.


WHOOSH 09-21-2004 01:14 AM

Starting Battery vs. House Battery
Garrett, there isn''t a different ''charging profile'' in the different form factors of conventional flooded batteries you are considering; they will charge similarly because the battery chemistry is (or should be) the same.

As you continue to work your way through Calder, I think you''ll find him also raising the question of ''battery switch management'' and whether you want that variable added to your new system. With the same basic question in front of me (but for a larger boat which needed, I felt, a larger house bank), I opted for a single house bank of 4 x 6V T105''s and a Group 27 start battery (all flooded). But the wiring plan I selected allows me to *never* need to change the battery selector switch so long as all batteries and circuits are performing properly. Consequently, I never risk e.g. running a start battery down along with the house bank because I forgot to switch back from ALL to e.g. ''1'' after doing a charge. I can start off the house bank, should that battery fail, by moving the Selector to ''2''...but otherwise, nothing changes, ever. I find this utility (and protection for self-inflicted wounds) to be very useful in the real world. It''s downside is that one needs to add an in-line sense circuit of some kind that can allow charging voltage to reach the start battery whenever the alternator is putting that extra cost is the price of the simplier, more user-protected set-up.

If this interests you, visit or give the folks there (in CT) a call and put your hands on one of Jack Csenge''s simple 12V block diagrams showing how this is set up. (This will be free, BTW). It''s simple, clever, and totally consistent with the wiring recommended for more sophisticated DC circuits (as e.g. adding wind power, an inverter/charger) at a later date.

What you doing is painful - to the wallet, the back and the hands. But it''s exactly the right kind of thing to do with an older boat, and you''ll forevermore be thankful you put your time, grit and money into this project. Good luck to you.


GarrettK 09-21-2004 06:40 AM

Starting Battery vs. House Battery

Thanks a lot!!! The diagram sounds exactly like something that I''ve been considering, but have been unbable to actually find a daigram showing the layout.

Nigels book seems very thorough, but I don''t quite know enough about electricity to feel 100% confident about a set up that I design. I''ll be getting in touch with them very soon.

Thanks again,


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