Theoretically, the formula for the watts you can achieve with your battery is...Watts = (Volts x Volts)/Ohms. Where the volts are the battery output (actual) and the Ohms are from the cart, atty, etc.
So...at 3.7 volts and 1.8 Ohms you would be getting 7.6 watts. At 2.5 Ohms, you would be...