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Discussion Starter · #1 ·
Trouble shooting what I think is a parasitic draw problem, or perhaps a battery not holding a charge. I returned from the airport after a two week trip to find my battery completely dead. I’d been previously told my radio was causing an excessive drain.

Any way’s I can’t find the source; I think it’s intermittent, but here are some numbers. I think these are completely normal.

Standard Drain for a battery: 50 ma
Amp Hours of my Auto Zone Battery: 39.865
Reserve Capacity of my Auto Zone Battery: Minutes
Reserve Capacity to Amp Hour Formula: Reserve Minutes * .4167
Parasitic Draw at 0 minutes: 380 ma
Parasitic Draw at 5-35 min: 140 ma
Parasitic draw after 35minutes: 10 ma

So my battery entered sleep mode by 35 minutes.

How long will these parasitic drains take to drain my battery?

140 ma Parasitc Draw (Before Sleep Mode)
282.7607143 Hours
11.78169643 Days

10 ma Parasitc Draw (After Sleep Mode)--35 Minutes
1178.169643 Hours
49.09040179 Days


50 ma Normal Parasitic Draw
791.73 Hours
32.98875 Days

So based on the manufacturer claims, my fully charged battery should last 49 days before it needs to charge, but when I showed up at the airport, it was completely dead. The battery is only one month old, and I don’t expect it to last 49 days, but I would expect to be able to start the car after 16 days. The temperatures went from 25 to 70 during that time.
 

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Discussion Starter · #2 ·
Also measured the VDC with alternator running, engine on and got 14.8, immediately after engine shutdown battery was 12.4 so seemed normal.
 

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Battery's not charged up yet, 12.63 is normal for full charge.

Even new, testing it would help just in case. Loads look OK - good testing there.
 

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As usual Sailor is correct. Here are the routine voltage checks I make every oil change:
ROUTINE VOLTAGE CHECKS:
-All voltage checks made at the battery terminal posts, not at the battery terminal post connectors)
- Check resting battery voltage, optimal is >= 12.6 Volts (engine off for 4 hours)
- Check charging voltage 13.5-14.5 Volts with all accessories on and engine at at 1200 RPM
- Check cranking voltage (>= 9.6 volts)
- Check voltage drop across positive & negative battery cables. (<= 10 millivolts)
- Inspect connections all battery cables.

Believe it or not the difference between 12.63 and 12.4 is significant. Your charging voltage is good only if it was made with ALL accessories (hi-beams, radio, wipers, defrosters, etc) on and the voltage check was made at the battery terminal posts.
 

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Discussion Starter · #5 ·
Sailor and Milton Thanks.

Question about the voltage drop--How do I measure that? Is that AC or is it the difference between the terminals and connectors or something else?

Cranking voltage is 10.6.


Sidenote:
======

I got a solar trickle charger, a Solargizer I just finished installing. I don't expect it to fix the problem I'm having now, but I do expect the next time I leave my car parked for a few days for the battery to be good when I come back after I finish this problem. You can tell if the charger is working or not by a LED indicator on the electronics.

Some milliamp stats on the solar panel output being measured across the wires with no load attached on a cloudless day at 10 am:

Outside Flat to the ground: 210 ma
Outside moved towards the sun: 384 ma
Inside car flat: 50 ma
Inside car moved towards sun: 65 ma

LED Indicator remains lit no matter where placed. Just like the instructions say, a windshield absorbs the UV rays that operate a solar panel. That's why the inside amperage is a fraction of the outside amperage. So for this thing to work correctly, it needs to be installed outside the car, just as the instructions say.
 

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Here is how to find a parasitic leak. Disconnect the negative terminal of your battery. Attach the milli-ammeter between the negative terminal and the negative lead - with the milli-ammeter on the highest range - like ten amperes (if that is possible) Open the door of your vehicle and verify the light comes on and the ammeter reads about one - three AMPERES. The lower the ammeter range switch or connection to read milli-amperes. If you get a reading like 100 ma - or so simply remove the fuses one at a time until the milliammeter reads zero. - You'LL need an assistant to watch the meter as you pull out the fuses - but keep going until the milliammeter reads zero. The fuse you take out that causes the zero reading is where you are loosing the current (ie Juice) from your battery.

Oh I almost forget - sometimes if the space between the battery posts ( + & -- ) is wet or damp, you can loose the charge across the top or sides of the battery depending on if it is a top post or side post. Try wiping the space between the posts with a paper towel or cloth.... and good luck...
 
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