macho_mango

definitely sounds like your battery is lacking venting. Most cheaper batteries just sort of seep acid from the sides over time, or vent directly to the atmosphere. Most higher end batteries will have a vent that connects to a drain tube -> this allows acid evaporation to drain away from your battery and avoid eating new holes in your battery tray. I have an interstate 85 battery, and it has the vent. Davidson armored batteries are also vented. I'd recommend a vented or dry cell battery just to avoid putting more holes in the battery tray (and passenger side leaks!)

ExitWound

I had the battery charged up two days ago. I was reading 12.8V across the terminals. Today, I went to attempt to start the car, and it was reading 11.8V. That means I lost a whole volt over 2 days...which just isn't possible. Why do I say that? I have a 61mA draw on the battery. I disconnected the stereo and amplifier and I have a 59mA draw.

If the battery is rated somewhere around 50AH (say), I should be able to see that a 50mA draw should last ~41 days before the battery is too weak to start the car. (forgive if the math isn't correct, but the idea is sound) There's no way that draw can lead to a 1V drop in 2 days.

What's happening?

jpk

Reading the voltage while the battery is not under load is pretty useless; it's not a very good indicator of charge level (unless you got something like 9 volts and you know it's pretty much dead) You'll get much more meaningfull numbers if you switch on the lights and heater fan. You shouldn't see much more than a tenth or two difference between no load voltage and loaded voltage.

If you can park near a plug, just get a trickle charger (battery tender type thing - Lowes usually has one for like $20) and don't worry about it. If you can't plug in, think about a disconnect.

pontifex4

My guess is just that you're seeing the effects of Cold weather. Did the battery start the car? Also, did it start the car easily at 12.8V?
Edit: also, unplug your lcd clock and see what kind of a draw you have, then.

ExitWound

As I turned on the heater blower and the lights, and monitored the battery voltage, it went from 12.3 (where it currently was in the charge) plummeted to 11, 10, 9, in a matter of 10 seconds. What does that mean?

Edit: LCD clock has been unplugged for a years. It was draining the battery like crazy way back.

jpk

Voltage dropping like that means the battery is no good.

pontifex4

Wow! Yeah, unless you have a ground which is shorting more and more the harder you lean on the car, your battery is toast. Was it fully charged when you got it?

Back to my previous question, too: did it start the car easily when you first put it in?

ExitWound

The battery is 2 years old in the car, bought from Advance Auto. It's a EverStart 58R-3. Says "shipped Mar2007" but I've had it less than that.

The battery's always worked fine, as far as I know. Car's started fine when charged and when the air temp is warm (>30F). I don't know if 580 CCA is enough for central PA in the winter to be honest. But as far as I've remembered, the battery has always acted like a battery.

What ways can a battery drop voltage at such a high rate? What are the conditions required for that to happen?

pontifex4

Depending on the cell, you can see that from overcharging (if, for example, you had it on a charger which pumped 10 amps into it for a whole day after it had charged) and from freezing when _way_ undercharged.

These are pure guesses in your case, obviously. That it falls so flat so quickly under load, yet measures 12.8V with no load suggests that the problem wasn't internal resistance from overcharging. I'm sure users with more car battery-specific knowledge can chime in on this, too.

jpk

Sitting unused for any period of time without a full charge has very detrimental effects on a battery.
As the charge goes down, the sulfuric acid electrolyte breaks down into sulfate and hydrogen. The sulfate gathers on the lead plates, and will stay there until the charge is replenished and it gets forced back into sulfuric acid by bonding with the hydrogen molecules in the water.
If the sulfur gets to stay a while on the lead plates, it hardens into lead sulfate, and doesn't want to break back down upon charging. This reduces the available area for the normal chemical reaction and reduces the battery capacity. It doesn't take very long for this to start happening, a matter of hours sitting partially discharged will have some detrimental effect. Extreme cold or hot weather makes things worse.
High frequency "pulse" chargers are pretty effective at turning things around and breaking down the lead sulfate, but the best thing you can do is to always keep it at full charge.
I have a ten year old battery in my truck. There are times it sits for up to two weeks without use, but it has a hard wired battery charger and always gets plugged in. Same goes for the Porsche. With a full charge, the battery will never freeze and I know I have the juice it takes to start a cold engine.

ExitWound

A followup for anyone interested.

I cleaned up all the terminals with a wire brush, along with the insides of the clamps. I connected new grounds having bared them down to metal. I charged the battery in the car up to 12.8V and left it there for 2 days. I came back after those 2 days to a 11.8V battery. I measured the drain on the battery with nothing on and it was 60mA, perfect for a 944. The math didn't add up. I can't lose one full Volt over 2 days at that drain rate.

I took the battery out of the car and recharged it in the house. Back up to 12.8V after a few hours. I put the voltmeter on the battery and could watch it trickling off 12.79, 78, 77, 76, 75, 74....

I took it to Advance Auto and they tested it for free. It returned "12.3V - GOOD BATTERY - RECHARGE" and I told them that's not possible, that it was at 12.8V just 10 minutes ago. They offered to do a 4-hour full charge on the battery. I said sure.

Picked up the battery from Advance Auto. After 4 hours of charging, we tested it and it read 12.3 RECHARGE and even they were puzzled. They think maybe there's a broken plate as if the battery froze and cracked one of the plates. They also showed me how to pop the top on the battery and check the levels of liquid. 2 of the 6 cells were a little low, but nothing crazy.

It's under a 72 month warranty from WalMart. I have to hunt down the receipt and see what I can do (which isn't going well, even though I thought I knew where it was).

I know freezing batteries are possible if the battery isn't charged. It's been sub 20F for weeks here in PA. If the battery wasn't charging due to the corrosion which started this thread, do you think that the battery could have frozen and cracked a plate?

Edit: 24 hours later, it's at 12.26V. So it's holding charge at 12.3, just no higher.

Grandpa#3

Off the subject a wee bit, but finding receipts for things bought with a warranty. A small two drawer filing cabinet is an amazing thing to keep all important household papers in one place. A folder marked for what is in it and it is easy to find. I had to do this just so I could find things. I tend to put things up where it is safe. It's safe alright, so safe I could never find what I was looking for. I have a folder for each car, truck, horse trailer and even my tractor, not to mention all tax receipts.

Cheers,
Larry

ExitWound

I normally do that. I have all my tax receipts in one drawer, and other important documents in the other. I keep all maintenance for the porsche in the glove box. The little flap on the battery that holds the receipt tore, and I took the receipt out and put it in a safe place. And I actually found that safe place a few months ago. But now, I can't remember which safe place it is! I've looked through them all too. I think maybe it may have gotten tossed by accident. :\