Battery Life

Benny · Jun 3, 2009

Snuffy, good news and bad news. For day sailing on a lake and the occasional overnight stay a single battery will do nicely. The bad news is that a "starting" battery is not designed for cycles of deep discharge and recharge and just a few of these cycles may render it useless. Since you do not need a battery to start the engine there is no need for a starting battery. You will be best served by purchasing a "deep cycle" battery. They have some at Walmart that sell from $60 to $80 depending on the size. Bigger is better a group 29 will give you around 115 amps capacity, while a group 27 will offer around 100 and a group 24 around 90. In order to maintain the life of the battery it should not regularly be discharged in excess of 50% of its capacity. This means that a group 27 with around a 100 amps should be recharged once 50 amps are utilized. You do not have to run the navigation lights all night if you are anchored. You may burn the anchor light if you feel its necessary. The anchor light may be burned from dusk to dawn or around 10 hours, the typical anchor lights uses around 0.8 amps per hour so you are looking at a consumption of 8 amps. The VHF uses 0.5 amps to receive and 5.0 amps to transmit. If you have it on standby and to receive for 10 hrs your consumption will be around 3-4 amps. If you transmit for 15 minutes you will have used less than 2 amps. The depth sounder uses around 0.2 amps so if you keep it on for 10 hours you will have used 2 amps. You may use a fan for 12 hours for around 3 amps and some cabin lights at night for another 5 amps. In total you will have used under 25 amps so a single battery will be adequate for your overnight trip.

Joe · Jun 3, 2009

nice answer from Benny although I didn't see anything about the stereo... But, just to add on a bit... You could use the 4D lantern as an anchor light, or use it in the cabin for reading so you didn't have to use the house lights. Another suggestion, get a hands free LED light, the kind you strap around your head.. A very handy device to have around the boat when you need both hands and the light is bad, such as checking the anchor...... I found a very nice one at costco for $20 that has white and red light plus a dimmer switch. I keep it in my boat bag... Use it all the time.

Jim Kolstoe · Jun 3, 2009

Another power extender is a kerosene lantern instead of electric lights for your cabin lighting. They give a soft pleasant yellow light. We have a bulkhead mounted light that I put a mirror behind to reflect light which would otherwise be absorbed by the wood.
Jim Kolstoe, h23 Kara's Boo

sailingdog · Jun 4, 2009

Joe Snuffy said:
Greetings all. I have a question about my battery life. I'm a lake guy in a Catalina 27. I'm a noob so to speak, and all I ever do is day sail. This weekend the wife and I plan to spend the night on the boat, so this means running the nav lights all night long. I have an outboard 9.9 pull start, so the battery just runs the VHF, lights, stereo, and depth finder. I have a single battery on board to run these. Usually a normal 6 hour sail is no sweat for the battery. The battery was a "deal" at $42 bucks for the "starting" marine battery. I cant recall the size and specs. I plan to hoist a 4D cell lantern fom the main as a backup, but do you think my battery will last the 12-18 hours of the cruise? Sure, I plan to kill everything but the nav lights before I go to sleep. Putting another deep cycle battery on board is not a problem, but as my sailing time is little, I have not spent the money.
Cheers!

It really depends on what the VHF, lights, stereo and depth finder all draw and what size battery you have and how fully charged it was to begin with. You don't state how many amp-hours it is. Are your lights LED-based or incandescent?? How loud do you play the stereo??? All of these factors will make a difference.

The fact that it is a starting battery is also important. As pointed out already, starting batteries don't really have the proper construction to deal with long constant discharges like deep cycle house bank batteries would.

If the battery you have is a group 24 starting battery, it is likely about 80 amp-hours in capacity. This means you've got 40 amp-hours of usable capacity, unless you don't mind running it down severely and killing it prematurely.

Benny's numbers are fairly good, but he's making the classic mistake of screwing up the units. The anchor light will use about 8 amp-hours, not 8 amps... The VHF will use about 6 amp-hours, the fan, 3 amp-hours and the cabin lights, depending on the number and kind, may be as much as 10 amp-hours, etc.

Yes, you will probably be okay—if the battery is fully charged to start with, but in the long run, you'd be better off getting a deep cycle battery and a battery monitor, to better get an idea of what your actual battery usage and charge cycles are like.

Battery Life

Joe Snuffy

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Benny

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Joe

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Jim Kolstoe

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sailingdog

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Joe Snuffy

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