do you facing problem with charging 2x3.7v battery connected in sereis.here is the simple solution.
Step 1: Needed Parts
you need the following things-
*2x 3.7v li Ion battery
*2x resistors(330 ohms)
*1x6 volts relay
*1x6 volts zeener diode.
Step 2: Circuit Designing
I have designed the circuit in droid tesla pro.
It works in the design. now its time to test it practically.
Step 3: Constructing the Circuit.
first make the series connection. then make the led connection.
second make parallel connection.then connect led with resistor.
third connect the relay i used jumper pins to connect them.
switch to series after connecting the relay now. See reason for connecting relay to the circuit in next step.
Step 4: Theory Behind the Relay !!!
There is no problem in connection when it is in parallel. But when the connection is in series one of the battery is connected to the parallel output and there you will get 3.7v output at the parallel output.
So, to solve from this problem connect a 6v relay to the series output of the circuit in parallel with a 6v zeener diode.
this will cut the connection of battery from parallel output when the batteries are in series connection and when the batteries are in parallel relay will reconnect the battery.
Step 5: Note:
The 2 switches in the circuit is the one switch shown above.
now one click to change the batteries from series to parallel.