New battery 7 months ago but car left sitting

  • 1998 FORD RANGER
  • 92,000 MILES
New battery 7 months ago but car left sitting. Tried to jump. After 15 minutes hooked up the radio and dashlights/headlights worked and ignition clicked (rather than nothing) but still wouldnt start. Help?
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Wednesday, December 12th, 2012 AT 4:46 PM

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You need to charge the battery WAY more than 15 minutes. All vehicles from that time period can draw up to 35 milliamps, (.035 amps), to maintain the many computer memories. Chrysler says at that rate a good battery will still crank the engine enough to start after sitting for three weeks. That is the industry standard for a new battery, so we can assume nothing else is wrong with your truck.

After seven months the battery will be completely dead. It will take ten to fifteen minutes on a battery charger before the acid becomes conductive and the battery begins to take a charge. If your charger has an amp meter, you will see the current start out at nearly 0 amps, then it will slowly come up as the battery starts to take a charge. After about an hour, the current will go back down as the higher battery voltage opposes the charger's voltage. You can consider the battery fully charged when the current drops to around five amps.

This isn't so important with a newer battery, but when they get to be two to four years old you should never charge them at a high rate. Your generator puts out three-phase current which is very steady. Home battery chargers put out rectified single phase current which goes from 0 amps to maximum amps 120 times per second. That pulsing current vibrates the plates in the battery and will accelerate the natural flaking off of the lead. When enough has flaked off and collects in the bottom of the cell, it shorts the plates and the battery must be replaced. The simple solution is to always use battery chargers on low charge rates to prevent overheating them and to delay the inevitable shorted cell. Give it a good hour on the charger.
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Thursday, December 13th, 2012 AT 12:34 AM

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