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At about 20°C, there has been a situation that the OEM battery in my '08 Jetta was not capable of starting the car at all (virtually no movement of the starter at all), after being used for at least an hour to charge a cell phone and open/close the power windows with the engine not running.

However, leaving it alone for some 15 to 30 minutes, and the car started just fine.

Why does this happen? I thought the surface charge is generally only something that is positive compared to the overall condition of the battery.

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  • I have no "scientific" proof of this, but my experience with batteries is that they have what I would call a rebound, where they're quickly discharged, then after they sit for a period of time (with no power draw), will regain some charge. I've never heard of one getting enough power to start a vehicle, though. There probably is a scientific reason for this, I've just never found one.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Dec 8 '14 at 19:05
  • @Paulster2 The general term for such an effect on batteries is "recovery effect". For automotive batteries, I think the Kinetic Battery Model offers a good explanation - doc.utwente.nl/64556/1/BatteryRep4.pdf . Do you think there is a protective circuit preventing the cranking while the battery is under potential?
    – chilljeet
    May 6 '15 at 5:46
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    @chilljeet Can you populate an answer with your comment? Your article seems like a good source for an answer.
    – DucatiKiller
    Jan 4 '16 at 20:02

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