Slow drain

Ever since I got my XJ, it has had a slow drain on the battery. Today, I noticed the starter was dragging really bad. Put the battery on an automatic trickle charger, it instantly read full charge, the jumped about half-way down the battery gauge on the charger, the jumped back to full charge. It continued to do this until I disconnected it. Put a volt meter on the battery. 12.47 volts at the battery, 12.47 at the starter relay, 12.46 at the starter. Cranked it up, 14.4 runnin at the battery. Starter still draggin real bad. Cleaned all the connections, no help. Put the battery from my boat in, almost threw the starter off its bolts it was spinnin so fast. So... if the battery is reading a good voltage, why is the starter dragging, but does not drag when I switch in the trolling motor battery? Secondly, does anyone have any tips on tracking down a slow drain in the electrical system?

Devil_Mutt said:

Ever since I got my XJ, it has had a slow drain on the battery. Today, I noticed the starter was dragging really bad. Put the battery on an automatic trickle charger, it instantly read full charge, the jumped about half-way down the battery gauge on the charger, the jumped back to full charge. It continued to do this until I disconnected it. Put a volt meter on the battery. 12.47 volts at the battery, 12.47 at the starter relay, 12.46 at the starter. Cranked it up, 14.4 runnin at the battery. Starter still draggin real bad. Cleaned all the connections, no help. Put the battery from my boat in, almost threw the starter off its bolts it was spinnin so fast. So... if the battery is reading a good voltage, why is the starter dragging, but does not drag when I switch in the trolling motor battery? Secondly, does anyone have any tips on tracking down a slow drain in the electrical system?

Click to expand...

First. To troubleshoot a drain, you need an ammeter. Then, you can see what you are dealing with.

Second. Just because your voltmeter reads 12.47 at the battery (I'll assume with the engine off and nothing on?), doesn't mean you're good to go. Ever have a dead battery, but the radio works? Same idea. Take a reading with your headlights on, maybe your blower motor on high too, and see what you get. It won't be 12.47, but as the load on the battery increases, the voltage inversely drops. But, by how much is what you want. That's how batteries are tested- by the drop on a given load, and the voltage after the load is removed. Is it possible that you have another issue, like say a bad connection somewhere? Heavy loads are susceptible to corrosion and the low impedance within the volt meter isn't. And, perhaps the difference in cranking amps is enough to get the starter to turn with more efficiency. Maybe your battery has an internal high resistance short in one cell, causing it to drain itself at a higher rate. All batteries have some internal resistance, which is where the old wise tale of not setting a battery on a concrete floor came from.

Take your battery to somewhere they test it for little or no charge. Use an ammeter, or something that can measure DC amperage, to find unwanted current draw.

on the subject of a current draw. Put an ammeter in line with the positive cable of the battery. Then start pulling fuses one at a time. WHen the current draw goes down you've narrowed it down to that circuit.

is there any current draw that will show on a system without a slow drain? Im wondering what king of diffrence will show once I find that fuse and pull it. Will the drop on my amp meter be a big drop or just a wiggle on the needle?