JoelD said:
I installed new battery and all is well.
Upon initial install she still had the same problem, tightened the terminals tight and all is perfect.
This is why I asked you if you were measuring the voltage on the battery terminals themselves, or on the battery clamps. If the terminals had shown the drop... then the battery was bad. If you were measuring at the clamps, then it could have been the connection.
JoelD said:
Afraid to test old battery for fear that it might have been loose positive terminal all along, I checked the ground but did not tighten up on the positive prior to replacing the battery. The bolt was badly corroded and weakened.
Learned valuable lesson regarding how tight terminals need to be.
Yup... connections need to be CLEAN and tight.
JoelD said:
Would be interested in the technical explanation, as a layman I would think metal touching metal would be good enough.
Joel
The current to the starter can be 200+ amps, so it takes very little resistance to add up to significant voltage drop.
As defined by ohms law:
Vd=IxR
Voltage drop = current (times) resistance
4= 200 x ?
? = 0.02 ohms--> Which is a tiny amount... too small for most home ohm meters to measure.
The gasses emitted by the battery are corrosive, this turns the conductive lead, of the battery post and connection clamp, into lead oxide, which is not conductive. The shiny silvery color is changed to a blackish dull color. Unless your connection is clean and tight enough.. the gasses will get between the battery terminal and the battery connection and cause issues. Sorry... this could have been your problem all along. Check out the old battery, it may be still good. But I suspect that since any current draw dropped the voltage down, you had a plate break internal to the battery causing a high internal resistance.
I hope you cleaned your terminal connections well before putting them back on. If you are lucky, then a wire brush is all you need to clean them up. If they are very black, you might actually need a sharp edge like a knife to scrape off the black lead oxide. Just be careful to remove as little as possible and keep the angle the same so it fits the terminal properly. It might also be a good idea to get either the protective pads you can put under the terminals, or the spray on battery protectant. Either will greatly reduce the chance of corrosion of terminals. Hope this helps and makes sense.