Battery dead, 3hrs later fine as usual.Why?

Question

After letting my car sit for 10 days, it seemed the battery was almost empty. It did crank, but you could count every... sin...gle... comppp...ression. The lights got dim with each try, and the clock lost its time. Finally, there was nothing more than the typical clicking.

Three hours later, I just gave it another try before removing and charging the battery. But surprisingly, the car started immediately, the starter had not even the slightest problem cranking the motor.

Temperatures were not cold, and rose from about 16°C to 20°C during that time. Sure, a warmer battery has more power, and a warmer motor is easier to crank. But yet, I'm wondering because it was not cold, and the temperature rise was low. The battery seemed completely drained, and the started the motor like every day. Oh, and the battery is not that old - maybe 18 months.

Any idea what could explain this?

Answer 1

I suspect it would be a good plan to check your terminal connections and other points associated with the power to the starter or solenoid. A poor connection in this circuit would present the characteristics you describe for a slow turnover and failure.

It's possible that during your attempts, the bad connection(s) heated up due to the high current and high resistance. When you ceased to attempt the start, the cooling of the connection could have changed the mechanical contact in such a way as to improve it. That's a bit of a stretch, but I've experienced nearly what you describe. It was discovered to be a loose bolt on the ground at the engine block.