constant 12v and constant 200mA from a li-ion battery for led

I want to make a circuit to drive 24 LED in a 4 series 6 parallel configuration.
i have a 3.7v 4400mAh or 7.4 2200mAh li-ion battery. To drive these led in this configuration in a very power efficient way i need 12v with minimum current of 200 mA

i tried a few circuits but they are very less power efficient due to resistive loads and the voltages and current values for the led are also very fluctuating.

is there any method of driving LED in a power efficient manner with such specification.

Do you really need 12 volts? Your 2 batteries in series would only give you 11.1 volts.

You need boost LED driver IC, since Vin<Vout.

Sample IC-FAN5333


FAN5333 support Arduino dim the light.

You can get this from eBay

Automatic buck-boost With charging Constant current&Voltage Power step-up/down 4-35V to 1.25-25V