Battery Replacement Revisited

[MarkSailor]

I am planning the replacement of the batteries on a 1995 Catalina 320. I currently have 2 4D flooded lead acid batteries, vintage 2003, with a rated capacity of 1000 CCA, and (I estimate, because it's not marked on the battery) about 125amp/hour rated capacity. Today, I would say the batteries have less than 1/3 the rated capacity, and if I start the engine after a 3 hour sail, the voltage dips low enough to blank-out my GPS/chartplotter.

The batteries are wired to a 1/2/both/off switch, and charged by a Lucas 55 amp alternator, or a Freedom 20 inverter/charger connected to shore power at the dock. I primarily day sail, but aim to do an occasional weekend or longer cruise. The big power users on the boat are 12V refrigerator and radar (if I use them, which is rare), Raymarine wheel pilot, and occasional stints on the inverter to run a microwave or DVD player for my 6 year-old niece. I have incandessant cabin lighting and the usual electronics/stereo.

My initial intention was to convert to higher capacity batteries - AGM or Gel, to increase available amp/hours between charges. But I am concerned that the high bulk charge acceptance rate of an AGM or Gel battery will burn up my 16 year old 55 amp alternator. Also, I have read that I shouldn't use Gel or AGM batteries on a charger that is not designed for them, or one that does not have a battery temperature sensor. While the existing inverter/charger (probably installed by Catalina in 1995) has dip switches to select for flooded or Gel cells, it has no setting specifically for AGMs, and no provision for a temperature sensor.

Based on all of the above, I'm thinking about replacing the existing flooded batteries with the equivalent new flooded battery, and using the 1/2/both switch to draw from one battery for house use, and start on the other one, just like grampa did. My thought is that the existing set-up will be more than I need for day-sailing and that if I find I need more power for weekend cruises, I could buy a dedicated 12V cranking battery and an echo charger -- probably for less than it would cost to repalce my existing alternator with one that could supply the charge capacity of the AGMs or Gel batteries. And if I had a dedicated cranking battery, I could double the useable capacity of the house batteries by running in "both" mode.

I have read seveal older threads where the consensus was to go with the AGM batteries, and I get that they are where technology is going. But I'm trying to avoid the cost of the new alternator after the new batteries burn up my old one.

Pardon the lengthy post. I know there is a lot of collective wisdom out there. If I am missing something, please tell me. Thanks in advance for your help.

[Stu Jackson]

Here are some thoughts on AGMs:

AGM Batteries - Making The Choice - SailboatOwners.com
Darn AGM Batteries - SailboatOwners.com


Not the best solution to charging requirements and systems on boats, especially if you're out on the hook. Very expensive lessons in those posts.

Try 6V golf carts and a separate start bank, or simply easier to carry 130ah wet cells 12V.

Here are some thoughts on wiring with a 1-2-B switch: Basic Battery Wiring Diagrams

[btrayfors]

Mark,

I believe your thinking is just about right for the type of sailing you do.

However, I'd add the start battery and EchoCharge sooner rather than later. This would allow you to use the 4-D's as a single bank which is much to be preferred.

Another possibility would be to add a good battery monitor like the Victron 600, and to always use the batteries as a single bank, both for engine starting and for house needs. This can work quite well providing that you keep an eye on the SOC, since even partially discharged 4-D's have plenty of oomph to start a small diesel.

Bill

[mitiempo]

I agree with Bill, an Echo Charge and a dedicated start (emergency) battery would be a good addition, the Victron monitor as well.

I would stay with flooded batteries.

But I wouldn't use 4D batteries, which are both not as heavily built as 6 volt golf cart batteries and not designed as true deep cycle batteries either. Also they are a bear to move around. A pair of golf carts will give you between 220 and 240 AH which is more than a 4D will. If you want/need more AH you can get 4 golf carts.