dead battery

hankster · Posted: Wed Apr 24, 2013 7:03 am Post subject: dead battery

my battery seems to drain when left awhile. how do I trace a short? or just put a disconect switch in line?

Levitation · Posted: Wed Apr 24, 2013 7:22 am Post subject:

First disconnect the positive cable clamp and move it aside.
Next put a charge on the battery - use a charger with an automatic trickle mode and let it charge and then go into trickle - overnight, or longer.
Unhook the charger and leave the battery disconnected. Measure the voltage (it will be above 13v right after being on the charger but will slowly decline as the surface charge dissipates)
Measure the voltage every day for a few days and see where it stabilizes. It should stay 12.68 or higher (higher is better). If it is below 12.6 after a day or three, it is time for a new battery.
If the battery tests good then you need to find where the leak is in the boat. Buy or borrow a clamp on ammeter for DC (Sears has a good one). Use that to trace your slow discharge load.

jerry97230 · Posted: Wed Apr 24, 2013 10:58 am Post subject:

For leak testing, I like to put a 12v light bulb in series with the battery cable.
If the bulb glows, you have something trying to draw power, disconnect things until the light goes out.

Jerry C Nile

thataway · Posted: Wed Apr 24, 2013 1:07 pm Post subject:

First all boats should have a switch between the battery and any of the positive bus bars, circuit breakers or engine cables.

I really recommend a second battery as a back up--and that way you can run the electronics without subjecting them to low voltage or high spikes.

Many items on a boat have a parasitic draw--radios and some GPS have memories, the bilge pump may be one which comes on every few minutes and checks for water. There can also be minimal shorts due to corrosion.

I certainly would test the battery--and might even go a bit further than Denny-o, by load testing it.

If it has been run down, less than 11 volts, it will damage the battery. I would buy a new battery, along with a switch, before even starting the tests.

A light will work to see if there is current flow, but with very low current it may be very dim or even not visiable. Try the light first in series with the positive lead. If that does not light up, I would then check with the volt meter. Most have a 10 amp circuit--separate from the low current flow which is measured in milliamps. You have to plug the red lead into the special socket. For example one in-expensive volt meter I carry in the boat is the Sperry DM 4100A You can find them for about $15, and the manual is at: http://www.sperryinstruments.com/documents/products/dm-4100a.pdf

There are more expensive clamp on meters, but first using the light, and then this type of in expensive meter it will give you a good idea of how much current draw there is.

Ted Osborne · Posted: Thu Apr 25, 2013 1:51 pm Post subject:

The Lowrance GPS/Fishfinder I have needed to have a cutoff switch installed even if you turned off at the machine. If not installed it will remain on. Bob also made a subtle mention of that.

colbysmith · Posted: Thu Apr 25, 2013 10:36 pm Post subject:

Some of the newer bilge pumps draw current all the time also.

Wandering Sagebrush · Posted: Fri Apr 26, 2013 11:42 am Post subject:

BrentB · Posted: Fri Apr 26, 2013 11:53 am Post subject:

How old is the battery?
Has it been tested?

Captains Cat · Posted: Fri Apr 26, 2013 5:56 pm Post subject:

hardee · Posted: Sat Apr 27, 2013 1:01 am Post subject:

In my case, I have an AM-FM-CD stereo that has a VERY low level light that remains on even if it is turned off. It was too dim to see in the daylight and it cost me a battery before I found it. I learned to remember the total power OFF switch. It works.

Harvey
SleepyC Moon