I have a small 1S 3.7 volt 110mAh Li-Po battery that uses a charger that runs off of four AA batteries... I'm not the biggest fan of using batteries to charge a batttery, so I wanted to modify the charger to accept DC power from a AC Wallwart. I plan on using a Power Jack w/Switch so that it will use batteries when the wallwart power plug is unplugged and cut off the battery supply when the wallwart power plug is plugged into the charger.
I got a 6v 1A wallwart that I ordered off ebay for a whopping $3 (shipping included!). Great deal huh? Well I used my meter to confirm which wire was the positive, and to my surprise, the voltage was 9.75 volts! I'm gonna fry the little sucker or expode my battery with that kind of voltage! I was thinking that I could either use a voltage divider by putting two resistors in parallel or using a bunch of diodes in series to drop the voltage to 6v.
1. Am I correct in that 9.75 volts is too much and I need to drop the voltage?
2. What is the best method to drop the voltage?
a) a voltage divider using two 1/8 watt resistors
b) a bunch of diodes in series
c) something else I am unaware of
I've aslo heard that some cheap wallwarts put out larger voltages until a something is connected, then it settles down to it's stated voltage output. Is this true? If so, should I just connect a resistor and LED inline to get the voltage down?