For some reason I'm not finding a discussion on this, even tho I know its a constant topic. My '97 XK8 sits in the garage for weeks or months without being started, sometimes causing the battery do go just dead enough to not start. It has enough to keep the clock running, but not anything else. I have replaced the battery twice (warranty) because of this. I have used a trickle charger at times, but that's a pita to do constantly.

Yesterday I took it to be smogged (CA). Of course, it needed a 30 minute charge at 60 Amps and it started. Of course it wouldn't even send enough info to the smog computer to do a test. I drove it around for over 50 miles of combo driving. It still wasn't picking up several key signals. During the drive my son noted that the amp guage needle never moved into the + side. OK...but at several points it did show a discharge condition. A/C and lights on, so I shut them both off.

I drove it twice today with no problem starting. Amp needle in the middle. When I got back I left it running and checked the voltage. 13-13.86v on the battery terminals. My other vehicles show about 14.5.

Am in the normal charge range, but the guage is only showing a "neutral" position because the battery is fully charged? Then, why does it keep dying....to the point it "FORGOT" all the emissions information??

 

Check to make sure the flap is shutting when you pull the key out. If it tends to stay only half shut it will not shut off all the little gremlins that steal your volts. Give it a shot of WD40 or a key lock lubricate and listen for the click when you pull out the key.
Wayne

 

I have a scan gauge in my car to monitor water temp and voltage.

On startup my voltage runs around 14.2 for a short period and then drops to around 13.8 as long as the car is running no matter what is on.

With the car off my voltage stays around 12.4 with nothing on.

 

Checking and lubricatiing the ignition flap is good advice.

The 'gauge' is a supposed voltage gauge, not an amp gauge. Nevertheless, it is 'fake', just like the coolant and oil pressure gauges and does not reflect reality. It is just an appeasement for the driver.

These cars can take hundreds of miles to go through all of the emissions tests, but you can speed it along a bit by keeping your fuel tank between 1/4 and 3/4 full and include a few of 15 minute idling periods. Many OBDII readers will assess emissions readiness without visiting the emissions test station.

The low voltage at the terminals is probably due to the fact that the battery is still charging, but it is high enough to indicate that your charging system is probably OK.

With the type of usage you have, you would be better served with an AGM battery and/or a battery maintainer (not a trickle charger). Ordinary batteries die early when allow to discharged during long periods of non-use. AGM batteries are much more tolerant of this. Otherwise invest in a CTEK 3300 maintainer, with a 'comfort extension' to make it a quick matter to plug the car in when leaving it parked.

 

Many cars need a decent-condition battery to run properly. If you don't use the car much you probably need a batt tender of some sort such as Ctek.

 

These cars do need to run often. I find the same situations if I leave my cat without play too long. In my case ABS, traction control and a few other light in the info center would come on.
I recommend 2 things if you can use them. Bought a Solar Battery charger from Harbor Freight ( if you have a similar store) for $ 13.99. Works great. U can leave on the dash as it has a cigarette adaptor or hook to the battery like I have. In my case I have a window right near the trunk. Puts back just enough juice for the electronics/ alarm. Fluctuates enough day/ night, etc not to over cook battery
2nd item, scan gauge. monitors constant charge as well as pretty accurate engine temp. Can clear check engine lights and reports codes. Rich

 

Allowing a battery to discharge completely then hitting it with a 60 amp boost will kill it in short order.

Charging voltage from the alternator will fluctuate according to engine speed, load and battery state. Comparing to other vehicles is almost meaning less.

If you're going to let the car sit for more than a few weeks, get a battery tender and leave it connected at all times.

 

Thank you all for your answers. I'll drive it again today and drop by the shop for a hook-up to see if the sensors will all show up on their new computer. And, I'll get out my battery tender (with auto shut-off) and use it.

 

I did see that the little flap on the ignition lock wasn't completely closed, so I gave it a couple of shots of WD40 and worked the key in and out a few times. Maybe that will help. Back to the smog shop today....hope it's all recovered and ok.


UPDATE: Passed smog....got penalized by CA DMV $21 for missing the renewal date by 1 day. Talk about money sharks. What's that....$21 on a $82 renewal fee.....about 25% a day? People used to get arrested...or beat up...for charging fees like that.


Anyway, it's done. But I did something stupid and broke my antenna off. I'll search and start a new thread.