How long until battery's dead??

I have an anti-theft device on my '01 PT Cruiser. You have to turn the headlights on to start the car. Which is fine until you forget to turn them off. Today I forgot and I shut off the ignition. About 40 minutes later I noticed they were still on. I tried to start the car, it cranked about three "whirls" then "click, click, click..........." I charged the battery and then went and had it tested. It tested as being fully charged and in good shape. Seems to me that the lights should have not killed the battery in this short of a period of time. It's the original battery, I guess I should replace it before the weather turns cold. How long should a fully charged battery be able to keep the headlights on and still have enough current left to start the engine??

Reply to
tomkanpa
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The original battery in our '96 Stratus lasted at least 5 years, IIRC.

How many Watts are the headlight bulbs on the PT Cruiser? Let's say 60W each; that's 10A for the headlights. Plus another 2 or 3 Amps for the rear lights, perhaps. Even if we say 15A, I would expect the battery to keep them running for 2 to 3 hours -- but whether there would still be enough left to start the engine at that time is another story.

Perce

On 08/28/05 02:43 pm tomkanpa tossed the following ingredients into the ever-growing pot of cybersoup:

Reply to
Percival P. Cassidy

I have had a brand-new high-capacity battery keep headlights on in my wife's car for 8 hours then still start the car afterwards.

I think your battery is probably still good but is nearing the end of it's lifespan. You may have some corrosion on the terminals - take apart the terminals and give them a good brush with a battery post brush, or better yet remove the battery, clean the top off with a hose, give the terminals and clamps a good brush, put it back together and spray on the battery corrosion inhibitor.

A deep discharge on a car battery like leaving the lights on once or twice generally won't hurt it if you charge it up again right away. Repeated deep discharges will shorten it's life

Ted.

Reply to
Ted Mittelstaedt

Interesting how different this is with lithium ion and other 'solid-state' batteries for gadgets.

BTW, it's "its", not "it's" in your sentence...:-)

DAS

For direct contact replace nospam with schmetterling

Reply to
Dori A Schmetterling

You can buy marine lead acid wet cells that are the same form factor as car batteries that will take repeated deep discharges with no problem, people use them for trolling motors, etc. They are not good for starting cars, however.

From what I understand this problem isn't specific to lead acid batteries in general, it is specific to car batteries because their plates have been modified to optimize the ability of the battery to dump immense amounts of current into the starter for a short period of time. There is some kind of mechanical or chemical tradeoff that is made there which limits the ability of the battery to be drained down past 20% of its capacity on a repeated basis.

The only problem that is specific to lead acid batteries, and affects all of them from Optimas to UPS gel-cells, is that if they are stored discharged for any length of time with an electrolyte in them, the plates will sulphate and the battery will be destroyed.

Sorry about that, it is one of my blind spots in writing.

Sigh.

Ted

Reply to
Ted Mittelstaedt

current into the starter for a short period of time. There is some kind of mechanical or

That's interesting. When I last researched batteries about 10 years ago or more, I found that of all of them, the lead acid batteries were most likely to come back from deep, deep discharge. Now this was in general, not for car batteries but for the lead acid batteries I would buy in an electronics warehouse.

Reply to
treeline12345

Right. Also note, that a discharged car battery is much more likely to freeze and the expanding solution will distort the plates and that alone will kill the poor thing.

Richard.

Reply to
Richard

Reply to
tim bur

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