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[billmathus]

A previous owner added 2 batteries - total of 4 - to my 1988 Catalina 34.  Two starter batteries, in parallel, have been added in the Lazerette, and two house batteries, in parallel, are located in the battery compartment under the forward salon table seat.  The wiring runs are somewhat confusing, but seem to work well enough. I am wondering if the added capacity is worth the loss of storage in the lazerette - not to mention the added weight in the stern.  I am considering going back to the original design, and keeping it all very simple.  Are two 27 series batteries (1 house and 1 starter) sufficient for everything onboard?(wondering why the change was made in the first place).  Any thoughts or opinions will be appreciated.

[TonyP]

Bill
We have a 12volt start battery 90 amp/hour, close to and behind the motor under the rear bed, as well as 2 x 12 volt 90 amp/hour, just in front of the sink under the seat. These allow the original Alder Barbour fridge freezer to work well as long as a couple of hours are spent running the engine each day. I do notice if iPhone/iPad charger left on overnight doesn't allow the fridge to make it till the morning. We will replace with bigger batteries when required.
good luck

Tony

[mregan]

It depends on what you are running every day.  I have 2-Group 31 for a house bank and a 27 for the engine. After 2-2.5 days at anchor with the fridge cycling off and on, radio on minimal lights at night, I need to recharge the batteries.  The fridge is the biggest energy hog.  Am thinking for next year to put a 3rd Group 31 on the house and relocate the engine battery to under the aft cabin near the motor.

[Stu Jackson]

Bill, what you're describing is more like a dual house bank system, with two batteries in each bank.  Two start (reserve) batteries is totally unnecessary for our engines.  The dual house bank arrangement used to be the norm in the 60s when there were relatively low electrical loads.  With the advent of boat refrigeration, and a daily house load of around 100 amps, the largest house bank, with a single small reserve bank battery, has proven superior.   You could do this by combining three of your four batteries into a house bank - same amount of lead, longer time between charges with the same daily load.  To learn more, you might want to noodle around in the "Electrical 101" topic.

[Ron Hill]

BILL : Look in "Electric 101" and make your self an electrical budget. 
If you do NOT have a fridge, you well may only need 2 GP 27 batteries.

A thought

[Clay Greene]

It really depends on how you're using your boat.  If you are day-sailing and coming back to shorepower each evening, your set-up is unnecessary.  But if you're spending a lot of time on a mooring or at anchor and running the fridge, you'll want a lot of house bank capacity. 

I agree with the comments above that two starting batteries is unnecessary.  We had two Size 27 batteries as our house bank and a Size 24 in reserve.  The Size 24 had no problem starting the M25XP engine.  It was isolated from the house bank so we never ran it down while sailing.  It charged off of the alternator and the battery charger through an ACR.  We left the battery switch on "1" for the house bank system and never had to touch the switch for any reason.  But I was always glad that the Size 24 was there in reserve if we ran down the house bank. 

If you are going with a smaller battery bank, you may also consider switching out all of your light bulbs, both internal and external, with LEDs.  You'll cut down your power consumption and get more light in the process.