97 f250. Only when I let the truck sit for two weeks. One week, it's fine but after two it doesn't have enough power to turn motor over. Then I jump it and let it run for a while and it's fine until the next time it sits to long (which isn't to often)
Does not look like anything is on (glovebox, ashtray or anything). Maybe a bad cell in battery is slowly draining it? I don't know how to tell if there is power draw on the system.
Thanks
Mike

 

Remove the NEGATIVE battery cable from the battery post. Take a test light and put one end of it on the now bare battery post and the other end on the now loose negative battery cable end. If the test light lights you have a current draw.

When doing the test make sure everything inside the truck is turned off and the doors closed. If you have a working underhood light, you will have to remove the bulb or else close the hood far enough to where the light would normally turn off.

 

if your battery is to small in the could weather that could effect it...I had to swap cause previous owner put a car battery and during the fall no probs but since the winter on cold nights it gives me some trouble...but I would suggest getting it tested at a local parts store or shop

 

as bear said, get your battery tested.
but modern vehicles like this do have a certain amount of "parasitic draw" like that, which will run your battery down over time. but a week shouldn't be long enough to run it down.
if you don't notice any obvious problems, you might consider hooking up a very low output battery charger, i think one common brand is the "battery tender", the goal is to keep it from going dead because we all know that running a battery dead is a sure way to kill it permanently, and at well over $100/battery, we hate to do that!

 

standard problem with newer vehicles. just because the ignition is in the off position, that does not mean everything is off.
radio and PCM memory draw are enough to kill a battery in a few weeks.

 

Modern?!? He said his vehicle is a '97!

Anyway, voltage, voltage, voltage. Get a digital multimeter.

Measure the voltage across the battery terminals with the engine running. It should be over about 13.5V. With everything in the turned off (headlights, fan, radio, etc.), it should be over 14V. Less than that, you have alternator problems.

Measure the voltage across the battery terminals with engine off and all accessories off. It should be over 12.5V if the battery is healthy and fully charged. If it's not, then remove the vent caps on the battery (most have 2 now, each covering 3 holes.) Measure the voltage (just stick the probes down in the holes into the battery acid--don't get it on you and rinse the probes when you're done) of each adjacent pair of holes (1-2, 2-3, etc.). The voltage should be right around 2.1V. If a pair shows a significantly different voltage (or 0V), then you have an internal short--replace the battery.

Now, switch your multimeter to read AMPS (or use an ammeter). Remove the negative battery cable and put one lead of the meter on the cable end and one on the terminal of the battery. Pull the underhood bulb. This reading should be under 100mA, preferably closer to 50mA or less. If the number is higher than this, pull and replace your fuses one by one until when you pull one the measurement of the amp draw drops significantly. That is your problem circuit if there is a parasitic draw.

Putting a test light between the battery and the negative cable is pointless from a diagnostic perspective.

Jason

 

yes, 97 is a modern vehicle with a computer, and a computerized radio.
older carburetor vehicles did not have all the parasitic draw the new computerized vehicles have.

 

I know 15 years old isn't THAT old, but I think there's a huge difference in the overall technology level of vehicles (related to their engines, that is, not the entertainment gizmos, though those are much advanced as well) from then until now. Memory in radios has been around quite a long time, and requires very, very little power--that would take many months to kill a car battery.

I've cranked full size trucks from this era with decent batteries after they've sat for over a year, so I think he's got a problem beyond "normal parasitic draw".

Jason

 

These trucks are not modern, really not any more complicated then something from the early 80s.

The KAM on an EEC-IV draws about 1.0-1.5 milliamps of current, your average modern radio only draws around 7 milliamps of current to keep the presets alive. With a 65 amp-hour truck battery, that's 318 days worth of reserve power until the battery is dead, not including self discharge of around ~10%.

I suspect a failing battery or something's using more power than it should.

 

i have seen many newer radios draw up to 1 amp when shut off.
there is something in the ford radios that goes bad and will kill a battery in as little as 3-4 days.
disconnect the radio and the parasitic draw goes away.
i have replaced at least 50 of them in the past 8 years or so..

 

If a newer radio is drawing 1 amp turned off, it is faulty or was not actually off.