Battery drains down. Will not start engine.

[finish line 88]

115 hp 2 stroke mercury. Have 2 batteries on a perko battery switch. House battery runs GPS and live well air pump. Air pump is on a timer switch off 3 minutes and runs 30 seconds. New battery (size 24 600CCA) will drain down after about 8 hours running GPS and live well. Checked engine charging system and it is putting out 14.4 volts. Any ideas as what to check would help. Thanks

 

[bruceb58]

When you run the engine, which battery are you selecting with the battery switch?

 

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I m running the house battery (#2)

 

[bruceb58]

So when you measure the voltage of 14.4V, is that at the terminals of the house battery?

So out of curiosity, what is the other battery used for?

 

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Yes that volt reading is at the terminals. I use battery #1 as a spare start only battery. Had to use it last week to get back home.

 

[bruceb58]

What is the charge system rated for and what percentage of time in the 8 hours is the motor running?

 

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Not sure what it is rated for. Run time 2 hours. GPS draws 1.3 amps and livewell draws 2.1 amps

 

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Charge system is 16 amp

 

[bruceb58]

Your total average load is only 1.6A/hour. Even if you didn't run your engine at all, you shouldn't have an issue. I wonder if you just have a bad battery. If this is a starting type battery, I can see you may have a problem. The starting type batteries don't like getting discharged much and will lose their capacity as they get discharged deeply.

 

[Chris1956]

It does sound like you have some sort of short circuit. With engine off, disconnect positive battery cable. Put an ohmmeter or multimeter on the positive battery cable and the other probe to ground, in an Resistance measuring mode. Resistance to ground should be infinite, with all accessories and the ign key shut off. If you see some continuity to ground, perhaps your rectifier is partially shorted to ground, or some power and ground wires are melted together, or some insulation rubbed off a power wire?

 

[bruceb58]

Using resistance mode is not a very good way. Use the meter in current measuring mode.

 

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Not sure I understand how to use the meter in a current measuring mode with the positive cable not connected to the battery? Please explain Thanks

 

[bruceb58]

You want to do the measurement with everything turned off. Remove the battery cable and bridge the cable end with the battery with the 2 meter leads.
Put the meter in 10A mode first in case you have a huge draw. You likely have a lower measurement mode like 2A. You may have to move of the leads on your meter depending on what you have.

For this meter, 10A is on the far left input and 2A is the next one in.

 

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Thanks for the lesson. My meter only goes as low as 40 A DC. I am getting a reading of 00.39 to 00.40. So I take it that I have close to 1/2 amp draw somewhere ?

 

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When I checked battery #2 I had the battery switch on #2. I also went from battery #2 to the lug on the switch with same results. l also did the same for battery #1 and the reading was 00.00

 

[bruceb58]

When I checked battery #2 I had the battery switch on #2. I also went from battery #2 to the lug on the switch with same results. l also did the same for battery #1 and the reading was 00.00

When you tested battery 1 did you select battery 1 with the switch?

 

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Yes I put the switch to #1 and removed the battery cable and took my reading and it was 00.00. I did not take a reading from the battery to the switch lug.

 

[bruceb58]

So...that is very weird! Anything attached to your #2 battery cable that is bypassing your switch

 

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No nothing. The positive cable is a #2 cable and it is only 30 inches long. Could it be in the battery ?

 

[bruceb58]

It's not the battery causing 1/2A to be flowing all by itself if that's your question.