88 xjs, ever since i bought this cat, if i went a day or 2 without driving it battery would be dead. its a daily driver so no big deal, not often did i not drive everyday so it would useually crank. well its gotten bad real bad.
charge battery drive to work 3 blocks 7 hours later dead. jump, drive home charge battery, next morning dead. I have a black and decker smart charger with the alternator check on it (not sure how reliable) checked alternator and says its good. ***** and grins checked it several times says ialternator bad more that good. voltmeter fully charged battery reads about 10...11...or so when not cranked. Reads the same when cranked. no spike no increase. Looking like the alternator to me. All fuses that i can find are now out of the car. put the fully charged battery in couple hours later its dead somethings draing it i guess its the alternator. whats the chances of cleaning all contacts on the alternator to fix? Removal looks like PIA..PIA...PIA?????????????? tHANKS TO ALL, Doug if your out there you are my Hero.

 

Well first off if a automotive battery goes flat is is never the same. If it goes flat many times it is no good. My first reaction is you have a battery draw and your battery is now junk. Go buy yourself a new battery. Make sure it is fully charged before installing. It should be about 12.6 volts before installing. If it is less than 11 volts when you buy it return it for a fresh one. Once you have a fully charged battery, start the car. Measure the voltage across the battery terminals. it should be 13.5 volts or so. If it is not you have either a bad ground or a weak alternator. Clean all the ground point and retest. If it is the same, remove the alternator and either replace or have it tested and repaired.

If it passed the first test, turn on as many loads as you can. High beams, A/C, blower on high, rear window defog, and wipers. While all these are on measure the voltage at the battery. It should be at least 13.5 volts or so. If it is not increase RPMs to 1500 or so and recheck voltage at the battery. If it increase when raising RPMs then you need to clean your grounds or your alternator has problems.

If it passed both tests than you need to test for a parasitic battery draw. You need an ammeter and know how to use it for this test. If the draw is above 50 milliamps (.050 amps) than you have to find and fix the draw. Until you do disconnect the battery when you shut the car off, otherwise your new battery will be damaged.


Replace the battery with a good battery and perform the tests. Then report back and we can help if you need it.

 

tks will do...

 

BTW a Lead Acid battery with 12Volts across the terminals with nothing connected is flat (25% charge). 12.2 volts 50% charge. The battery should have at least 12.6Volts depending on the type Gel, Lead Acid, Calcuim etc.

 

voltage is completely useless for batteries. a good alternator will read 14 volts and 60 or more amps. 80 amps is typical GM alternator.

a bad battery will read anywhere from 13 volts to 0 volts. the only way to tell is amperage. a 13 volt battery can be totally bad, run all the accesories and lights, but not crank a starter.

 

Thats not right, AMPS is a variable depending on load Voltage is Potential energy. The charging circuit must have more voltage than the battery it is charging otherwise no current will flow to the battery and the battery could discharge through the charger.

A Lead Acid battery has 6 cells at 2.1Volts per cell this makes 12.6Volts yes it could be higher and will vary depending on the accuracy of the meter used. But a battery at 13.0Volts open terminal voltage WILL NOT be flat.

 

maybe not, but ive personally seen batteries reading 12 volts that werent worth their weight in lead.

 

At 12.0V a lead acid battery is flat as my post said

 

I agree it sounds like the battery needs replacing, but it sounds to me like a slow draw somewhere is killing the battery. Usually a bad alternator will kill the battery in 1/2 a day (in my experience anyway) so I'm wondering if it's something as simple as the light isn't shutting off in the trunk!

 

id think that too but all the bulbs are taken out in trunk area.

 

while were on this subject the radiator is now out, water pump out to get to alternator. when reinstalling these, is the tension on the belts (water pump, alternator) have to be precisely where they were? or just a good tension and close to where they were???????????

 

My power antenna was killing my battery, the PO had replaced the motor with one of the aftermarket replacements and the way he wired it in the motor was getting 12v all the time and "pushing" the antenna up constantly. Rewiring the correct way fixed it.

 

??? Why would you pull the radiator and WP to get to the alternator? Remove the air pump (10 minutes) and just unbolt the alt (another 20 minutes, only because you have to crawl underneath and loosen the tensioner)???

 

Well the rad had to come out to go get rodded, and my bad it was the air pump not the water pump.

 

OK, got it!

 

A battery no load voltage of 12 volts is a nearly dead battery. Obviously a load test can tell how much current the battery is capable of delivering. Also many of the new battery testers use internal resistance to tell battery condition. My point of discussing the battery is to make sure you start diagnosis with a good battery. A battery that goes below 10 volts will NEVER be 100% again. It more than likely will work for years but not at 100% of it's original specs.

Anyway you should systematically diagnose your vehicle rather than just randomly go at it. Install a good battery. Test the alternator as I suggested in my first post. This will tell you if you have an alternator capable of providing enough current to power everything. If you have an ammeter you can measure the output. Once you determine if your alternator is working properly or not than you need to perform a parasitic draw test. If you have a clamp-on inductive ammeter that makes life easier. If not when you hook up your ammeter inline have a jumper wire between the cable and the battery post. Then install the meter. Then remove the jumper. Otherwise the spike when connecting the ammeter may blow the fuse in your ammeter. You can do the test at either the positive or negative cable. Start at the 10 amp scale. Anything over .050 amps (50 milliamps) is a concern.