Parasitic drain on battery.
 

Battery went dead a few weeks ago. It's a year old, Duralast platinum.

Swapped alternator. Made a huge difference on startup noise, and I fully charged the battery.

Today I thought the dash lights dimmed on startup and life went on. Cleaned years and went to swap cars and dead battery.

Charging now. Any ideas? The current stereo has been in for over a year.

Be sure the alternator is putting out around 13.5 to 14.5 volts. Then, take off the neg cable to the battery and measure the amperage across the cable and terminal. It should be around .04 amps. If the current is higher, then take out fuses one by one and when the current drops, thats the cicuit with the problem.

If you just recharged the battery that went dead and are still using it, it may no longer be capable of holding a charge. I'd take it to an auto parts store that can do a load test on it. You may have to replace it. I find that my battery doesn't like to be left without being charged for more than about 2 weeks, or it drops to around 12 or fewer volts.

My charger said 25% when hooked up and said full charge in about 20-30 min at 10A fast charge. Seems odd, like it only has the top end.

Just check voltage with car running and batt unhooked to get alt voltage?

NEVER disconnect the battery with the engine running...

To check the alternator output, simply connect your MM across the battery terminals:
Engine / accessories off = 12.6v fully charged battery.
ditto 12.3v = half charged battery.
Engine running @ 1000rpm MM should read 13.5 - 14.5v depending on battery state of charge.
Anything less than ~ 13.0v suspect the alternator.
To sympathetically fully charge your battery, hook it up the the charger for at least 6-8 hours - preferably overnight @ ~ 2 amp trickle charge.
To check for parasitic draw, as per san rensho says above.

Sounds like some of the cells are dead or disconnected. Charging at 10A is a good way to warp the plates....

As Steve
 

No, no, no! As Steve said, never disconnect the battery with the engine running. Excess juice fries diodes in the alternator. Just put the meter on the + and - terminals while the engine's running. This will tell what the alternator's putting out, but nothing about the condition of the battery. Load test it.

On their website, Interstate Batteries recommends charging at a 10-amp rate.


"Step 3: Charge the battery at a 10-amp rate. 42 amp-hours needed by the battery divided by 10 amp charge = it will take around 4-1/2 hours to recharge the battery. (The best charger to use in order to charge a car battery is a 3-stage automatic 12 volt /10amp charger.) "

What Joe Said
 

That lead/acid battery is like a giant sponge or buffer to keep the pulsating DC being put out by your alternator from destroying the electronics in your car....including your ECU......DANGER DANGER Will Robinson.

The battery acts like a big filter capacitor and only smooth even DC is supplied to car after the battery.

PS on charging...I dunno about now (I suppose the laws of physics have not changed) but you charger lead acid batteries by voltage....you can put one on 13 V forever and never hurt it. How do you know you are charging at 10A ? Did you put an ammeter inline and measure the current ??

Don't put too much stock in the labels on Battery Chargers. Nicads you charge by current. If you are using a variable power supply to charge at 10A what is your voltage.....one must increase voltage to get higher current.

It is all right here

http://upload.wikimedia.org/wikipedi..._Pie_chart.svg

The charger has a selector switch. 2A slow, 10A fast, and 50A start. The 50A is not continuous and I don't use that.

On 10A it only took 20-30 min to go from clicks to "full charge" and green light on charger. Something's not right. I'll check volts tomorrow.

Tim, I've found that when my boat batteries get old and are ready to get rid of, they seem to take a charge quickly, but won't hold it for long and seem to have no storage ability. As I mentioned, your battery may be toast from going dead and need to be load tested.

What is happening is the internal resistance of the battery is rising due to plate sulphation over time. The higher internal resistance falsely confuses the charger into thinking the battery is fully charged when in fact it is not, and the charger shuts off.

Sulphation is a normal process in all batteries, but can be nearly eliminated by using a quality maintainer that has a de-sulphation step in the charge profile, which significantly reduces the build up, dramatically extending the battery's life, which more than offsets the extra bucks you spent for the better maintainer.

Im with you on that, the plates sulphate and film over with time and the ability to hold a charge gets to be less and less with time.....the plates also wrap with high current charges. I had an EE instructor put it in plain terms "Battery charging is like filling a wooden bucket with water,,,,you can fill it quickly with a firehose but you will never get it completely full and you will most likely damage each time you try....fill it with a trickle of water and it will fill to the top and last a lot longer."

I have also heard that if you run one completely down they will never hold a full 100% charge again

This.


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And I'll bet that's where I am at. It has been low enough to give just clicks twice now. I'll swap it tomorrow and look for a maintainer even though I drive it daily.

I may* have left the trunk open a few times and the frunk a few times.

*have no doubt I did

Ok. Battery has been to a couple auto places. Charged & load tested. Both passed it.

I don't have a tool that does amps through the leads. Just amp probe type. Those say about .04-.06A DC. Seems no major draw.

My tender says its 37% after sitting a week. Then it tops off in about 30-40 min with a 3A maintainer / charger. Brand new auto tend / charger.

Just tried all 3 testers. Newer one does say 1.3A across ground to neg post on batt. I'll track this down. Thanks.

Update. Pulled every fuse individually. No change.

Me, I'd suspect the alternator diodes and pull the connectors to the alternator and check again. Don't let them go to ground when checking or you'll smoke the electrical harness.

I did chase down a similar problem on a 72 Duster where we still had a leak with all the fuses pulled. In that case we were able to pull a firewall multiple connector and go pin to pin finding out it was a "seatbelt interconnect" box buried in the dash. We disconnected it and the leak stopped. Everything still worked on the car and we never did figure out what that box did other than draining the battery. I don't know where the harness production break is in the Boxster but I imagine there is one somewhere.

New alternator.

Never think that a new part can't be the problem