My (late) fathers 2000 Ranger has an issue with battery drain. Really nice shape, 40,00 miles. Sits in the garage most of the time. My mother drives it about once a week. She went to take it out a few days ago and it would not crank. We had this issue in the past. I took the battery to the parts store. They tested it and found it to be bad. So the battery in it is new in 2015. How does one test for drain down and then find the culprit? I'm going to charge the battery and leave it unhooked for a week and see what happens.

 

Might be helpful to know How was the old battery "bad"???? Was it just discharged, sulfated & wouldn't take, or hold a charge, did it have a shorted or leaky cell, cracked case, ect????

After shutdown & the computer puts everything to sleep over time, about an hour, so then our vehicles will have something like a 60ma parasitic drain on the battery, from things like the clock, memory in the radio & computer's & maybe from any after market add on.
SO, you could disconnect the B- cable from the battery & insert your multimeter in Series with the B- cable, with it set to the Amp scale & check it after an hour or so & everything should have gone to sleep & the drain should be around the 60ma figure. (Be sure to unplug the under hood trouble light)
If it's over 100ma, a door isn't closed, something isn't timing out & going to sleep, or has electrical leakage in a circuit, or a light isn't turning off, like the cab, brake, glove box, or under hood trouble lights. Or maybe an after market product has a problem, so be sure to disable them to see if the drain drops.
Before you begin the parasitic drain test, run this puppy by your favorite auto parts store for an in vehicle electrical system check up, to make sure the alternator diodes & new battery aren't leaky, or shorted. I've seen faulty brand new batteries, so try to think ahead, so as not to let Murphey's Law mess with you on the parasitic drain test.
Some thoughts for consideration, let us know how it goes.

 

You might 'wake up' the SJB or GEM if you disconnect the battery cable without jumpering a provision to 'hold' the memory. Using clips and jumpers, you can attach a 9-volt to the ground cable and a convenient ground while the cables are still attached.
Disconnect the battery ground, and connect the ammeter in series, red to the cable, and black to the battery post. With the meter in DC Ma or A mode, disconnect the 9-volt ground clip. Any load is now going through the ammeter. After reading, reconnect the 9-volt clip, remove the meter, and reconnect the battery cable terminal. Remove the 9-volt source. That should let the memory 'things' stay asleep, keep the audio settings & station memory, and leave the computer KAM alone. More or less.
tom

 

batteries go bad. Especially if you're only driving once a week.
If mom is starting the truck and driving a mile or 2 to the store and then starting the truck and driving a mile or 2 to go home.
Of course it's going to go bad because battery never gets fully charged.
You don't give any info so I am going to assume your old battery was original. LOL - pretty old battery.
I don't drive my ranger much anymore but the battery in my truck will go dead because my stereo feeds off the battery to keep it's settings plus my alarm system sucks the life out of my battery.
I keep my truck on a Battery Tender so it stays charged.
May be mom should do the same...
Deltran Battery Tender

 

The previous battery was not the original one. I can't remember the exact readout from the parts store test. I think the CCA was way too low. None of my stuff has chips or computers. I can go six months without worrying about whether they will start or not.

 

my opinion is the 1st thing to do would be see if the alternator is working/charging as it should - charge the battery on a charger then use a voltmeter to check the alternator reading when the engine is at idle

 

Thanks for the input, I'm going to check it out today.

 

Put it on the charger for 12 hours. Before charge: 11.50v. After charge: 12.75v. At idle after start up: 14.70v. Mom's happy.

 

OK, sounds like Mom needs to drive it more often & longer distances, or maybe come by & hook up a float charger to keep the battery topped up. You could rig it to plug into the cigar, or 12 volt power outlet to keep the battery topped up & help it last a Lot longer.
11.5 volts = 20% charge, so depending on how long it sat like that, the plates have begun to sulfate, so getting it to take a full charge & hold it, may not be possible, but a high quality float charger could pay for itself in a short time at todays replacement battery cost.

 

looks like you can rule out the alternator which is good... so... now see if the battery will hold that charge.

 

believe it or not pawpaw, but back in the day (ie. the 70's), my dad used to keep a carton of acid (not lsd!) in the garage for topping up batteries, along with distilled water.. which we used! a lot lol i don't think i have cracked open a battery in 20 years! those were the days.. but maybe they come back.. no?

 

I have several Harbor Freight float chargers around the place. They seem to do the job and even at the regular price they are under $10 IIRC........

 

Right now I'm looking at a battery tender with leads you connect to the battery side terminals. The other end goes out through the grille to a connector to the tender. This way Mom doesn't have to open the hood to take the pickup for a drive.

 

honestly the battery 'should' last a week without being charged/topped up. how are the temperature readings in the garage?

 

Ok, sounds like your about to have Mom all wired up for a fix on her wimpy battery soc problem.
We don't know how long it had been at the 11.5 volt soc, but if it was for some time, or if its happened regularly in the past, the battery plates are probably sulfated & may be self discharging.
Recharging slowly with the Battery Tender may be able to dissolve some of the softer deposits, but not likely to be able to have much effect harder thicker layers, so don't be surprised if she has to have the battery replaced.
Then the Battery Tender float charger can make that puppy last a Lot longer by keeping its charged topped off, so minimal sulfation takes place, If she remembers to plug the float charger in!!! lol