My wifes car decided to not start after she filled up. Turned out the battery was dead. My question is why couldn't I jump start her car with my truck and jumper cables?

I thought logically that attatching cables to her cars battery leads would allow it to start. Tried to start but it didn't work. I thought possibly the battery was absorbing all of the amps from my truck hence her car wouldn't start so I unhooked her battery and clipped the cables directly to her leads, no dead battery involved. This didn't change anything and I went and bought a new battery and her car started right up no issues.

So I'm baffled as to why her car didn't start when connected via cable to my truck's battery?

-CM

 

I've seen that before, its almost as if the computer is not seeing the proper volts. Yet you put in a new battery and away it goes. Can't boost it, yet a battery fixes it. Chalk it up to "new and improved".

 

I also had my volt meter with me and showed 13 volts when my truck was hooked up to her leads. And her "dead" battery showed 12volts but 2 of the battery cells looked dry.

-CM

 

That is very odd... sounds more like a computer glitch than a bad battery... 12V should be enough to crank... was there any power at all?

 

When my truck was hooked up she had power for all the electronics except the starter would only give a faint click and couldn't turn the engine.

-CM

 

Pretty common. When my wife's battery died...while I changed the oil...I couldn't start the car even with cables. New battery...fired up good as new. I don't know why, but if it is dead enough...even jumping it won't work.

 

Hmm.. that is very odd... I wonder if your truck didn't sense the load???

 

Keep in mind a good battery is somewhere around 12.8-13 volts. A battery at 12 volts is somewhere around 1/2 power or less. If voltage drops, you need more amps for the same power. The bad battery even with a boost could not supply enough power (volts) to the starter. Here is a nice web site on batteries it's about deep cycle batteries but still interesting. FYI http://www.windsun.com/Batteries/Battery_FAQ.htm

 

Good point about the current dropping before the volts do...once the volts are down...you are wayyyyy down on current. It won't start.

 

Buy good jumper cables and you won't have this problem.

 

Pretty common really, the dead battery is acting like a sponge and not allowing all the juice to get to the starting system. Let it charge for a couple minutes and it will make all the difference in the world.

Heavy, quality jumper cables can solve that problem

 

If the bad cell (or cells) were dead shorted, the old battery could absorb quite a few amps... and the connection made by typical jumper cables won't carry all that much.

 

what size is the wire in the cables???

I have seen people have problems out of a cheap set of 6 gauge cables, throw on my custom made 2/0 cables and fire right off. too much amperage for the cables to handle.

 

If the battery is good but you drained it do to leaving your lights on or something like that you can jump start it after leaving the cables connected for a short amount of time.

If the battery is dead and is bad you aren't going to get it going. The bad battery is sucking up all the charge you are putting into it and it shorting out.

 

make your jumper cables out of #2 welding cable or larger, instant start every time , well worth the time and money