Silly question, but isn't the battery a "Smart" battery and hence contains all the charging control inside the battery module its self?
i.e there arent any balance leads etc so that the charger can monitor the individual cell voltages.
I looked in the bottom of my charger, and it just says 12.6V at 4.0A. I don't think the mains charger is technically a charger at all, its a power supply.
I measured the voltage and it was 12.68V offload.
Has anyone taken a "car charger" apart to see whats inside ? Can someone measure the voltage on the pins on the output of the "car charger" and see if its 12.6V or just whatever voltage is on the car battery.
If you have a car charger, you could also use a multimeter to measure the connectivity on both the negative and positive side of the circuit. e.g. I suspect one pin on the battery plug probably goes to negative, (which I think is the outer of the lighter plug), and the other pin goes to the positive.
It could be that the "car charger" contains some voltage regulation to drop the car battery voltage.
e.g.
http://www.linear.com/product/LT1084
Definately sounds like it would be possible to build one much cheaper then they are selling them for.
Perhaps its a market opportunity ;-)