Quote Originally Posted by Zilli View Post
What i need to clarify is - when i am jumpin the battery, is the battery still what is being used to power the car? ie, is it still part of the circuit? or will the charge from the other car go straight past the battery and pwoer the car up?

not sure if this makes sense, but to picture it as a circuit, when you put the jumper cables on, does the power go through the system before the battery in the circuit or after?
No.

The jump from the car donor is only to give the old battery a boost to start up.

But if the overall voltage is less than 10v then its not enough to boost start the car - even if the jump car is being revved.

The old battery's internal electrodes need to still have minimal voltage/current & distilled water to keep its life and so that it can be spared for charging.

Otherwise if the electrodes are dry as an old grannys fanny.. Then bin that old batt and buy new.