After Jump starting a car; why do you need to drive it around?

[cosmosdan]

After Jump starting a car; why do you need to drive it around?
Um…Isn’t that why you jump started it?

[Rick]

@cosmosdan

After Jump starting a car; why do you need to drive it around?
Um…Isn’t that why you jump started it?

:smack: Why didn’t I think of that?

[Caractacus_Pott]

@Phlosphr

Quick question - I just bought an old toyota <snip> now if I leave it for more than 24 hours it needs a jump. Whats up with that?

I’m guessing from that sentence that after you jump the car in the morning, you can drive to work, park the car all day then drive home without a jump. Or that you could park the car, drive to lunch, park the car until going home.

Could it be possible that there’s something causing a drain that discharges the battery when the car is stopped? It may be a small drain that wouldn’t kill a fully-charged battery but may take your weakened battery below the threshhold needed to start your car after it sits for so many hours. You say you’ve recently bought the car so you may not have known the reason for the new battery. That could be it. After all, if you’re getting ready to sell an almost 20 year old car, are you gonna fix an electrical problem or just slap in a new battery and let the next owner handle it?

[HMS_Irruncible]

@Caractacus Pott

Could it be possible that there’s something causing a drain that discharges the battery when the car is stopped? It may be a small drain that wouldn’t kill a fully-charged battery but may take your weakened battery below the threshhold needed to start your car after it sits for so many hours.

That’s possible too; way back in the day I had a brick-sized cell phone which, if left plugged into the cigarette lighter outlet, would kill my battery after a weekend. (Just as an examples; I don’t think modern electronics would do this in a weekend, but I could be wrong).

[Dog80]

@Q.E.D.

That’s not entirely correct. It’s true that automotive lead-acid batteries don’t take well to being deeply discharged, but that’s due to the design of the lead plates. Automotive batteries have thin lead plates, because by using thin plates, you can pack more of them in the same space, thereby gaining a greater current capacity. The tradeoff is that the thinner plates will be completely sulfated–converted to lead sulphate–by the time the battery is fully discharged. Essentially, with little or no lead left, the process cannot be reversed, at least not easily (or completely). Deep-cycle batteries, such as used for marine applications are also lead-acid batteries, but these have much thicker lead plates. They don’t need to (and cannot) deliver the high current that automotive batteries can, but because of the thicker plates, the sulfation doesn’t completely consume all the lead, so that a much deeper and lengthier state of discharge can be tolerated. For recreational marine use, this is more important than high current, since the batteries will often sit for most of the year before being used infrequently.

Thick plates have another advantage. They are less prone to deformation. In Greece, the roads are full of potholes. The constant shaking causes the thin plates to elongate over time untill they touch each other at the bottom and the battery shorts and dies. It is not unusual for a battery with thin plates to die within 2 to 3 years.

The low cranking amp rating of those batteries is not an issue, since the temperature around here rarely goes below 5 degrees C.

[Mk_VII]

in older cars bad earth connections are frequently responsible for electric problems, and inability to charge (or hold a charge) is just one of them