I want to charge 2 series cells of Li-ion or Li-polymer batteries at 1.2Amp current and
battery rating:
1400mAh 8.4V battery
can you gimme any circuits (low cost) ?
you need a constant current source, and a shutoff circuit to kill the current source once the battery is charged. i'll get a circuit for you to use with a 12V supply that's simple (the current source itself is 1 transistor, 2 diodes and 2 resistors). the shutdown circuit might get a little more complicated.
A Lithium rechargeable battery with two cells in series needs a "balancing circuit" so that one cell is not charged higher than 4.20V then it doesn't catch on fire. All proper lithium rechargeable batteries and chargers have a separate balancing connector.