View Full Version : Battery Drain

Rowdy CY6
12-02-2006, 03:27 PM
I have two batteries that I use as my House and Engine Battery. I charged the batteries to full last week and now they are reading just over half charge. It seems like I have drain on the system. How can I diagnose and find a drain if that is what is happening?

Any info would be most helpful

Jay Greer
12-02-2006, 04:20 PM
If you don't have one, Harbor Freight is selling a 7 function multi meter for $2.99! You can use it to check your sysem for grounds or drains.

12-02-2006, 04:28 PM
A digital multimeter can be had for $15 anywhere. The cheapies won't measure amps though.

Got an auto bilge pump running a lot? Leave a light on somewhere? GPS?

Primitive Pete
12-02-2006, 05:59 PM
The easiest way to check battery draws is to disconnect both positive cables from your batteries. Then run a test light between a positive cable and the positive post. If the light lights up, you have a draw. Start pulling your fuses one by one, until the light goes out. That's the circuit with the draw. Re-install the fuse, then eliminate components from that circuit until the light goes out again, that's the component with the draw. A voltmeter can be substituted for the test light if you're feeling high tech.

Bob Smalser
12-02-2006, 06:55 PM
After you make the draw test as described and you find a draw, take a heat gun and carefully dry out switches and terminal blocks beginning with the ones most exposed to the weather. If the problem is new and the weather has been wet, it could just be a wet switch or terminal.

12-02-2006, 07:03 PM
Could the onset of cold weather have anything to do with it?

I had two car batteries go weak on me this week.

Rowdy CY6
12-02-2006, 08:07 PM
Thans so much for the suggestions. The batteries are new this season. I noticed this problem throughout the summer. My bilge pump was going on once every 12 hours on the mooring so that was not a huge drain. I will have to do some more research.

Thanks Again

12-02-2006, 08:45 PM
When you test for voltage between the disconnected cable and itís post use caution that all major circuits are open. If say the bilge pump happens to come on while testing you will turn your multi meter into a fuse!

12-03-2006, 07:45 AM
A decent test light is best for this mission, most good VOM's can go to 10 Amps dc and if your load is greater than that you will be changing fuses in the meter.

The only way to properly check state of charge on a wet battery is with one of these..
It could be your battery's are not being properly charged too.
If you are using AGM's than you will have to spend some decent money on a state of charge meter, one that includes a shunt to measure amp hours.
If you cannot find a drain using the test light method you will need to start digging on your charging system. It is possible that if the system is bad you may have fried a cell and the battery looks fully charged but only really carries a short capacity.
I did a boat this summer that had two fried 8d's due to the regulator going high voltage near peak charge. Same symptoms as you have.

12-05-2006, 10:40 AM
My $2.99 Harbor Freight multimeter does 10ADC just fine. Is it normal for your bilge pump to run every 12 hours? Is this a small vessel with a narrow/deep bilge or a big cruiser? On my 40-year old Connie the bilge pump comes on once per week at the dock.

12-05-2006, 10:41 PM
If no meter, one can serially pull the fuses in low lighting ... sparks will indicate circuit(s) in question.

Be aware that engine driven alternators (for batt charge) DRAW current at all times they are connected to the battery. A new one might draw only microamps; an old one in acceptable condition , maybe 70 miliamps. Sometimes one or more of the diodes in the stator output short , and i think it is they that then can cause an unacceptably large parasitic drain, probably requiring a replacement.

If Bob Smalser's heatgun trick 'works' , rinse the vicinity of the connection well with first fresh water (maybe tiny tad detergent), then rinse again with distilled water , then coat connection (after drying) with a (preferably synthetic) grease, or RTV silicone sealant.

>Could the onset of cold weather have anything to do with it?
Cold weather will severely decrease the efficiency (charge/discharge rate) of most all chemical reactions; will also force differential thermal expansion of varied materials in contact , as connections on printed circuit boards.