[Sammus]

Consider this:

Each pack is 7.4V with a capacity of 8000mAh, which means it can supply 8000mA at this voltage for one hour, or 8A for one hour, or 80A for 1/10th of an hour, or 120A for 1/15th of an hour = 4min = 240s. Now 120A @ 7.4V = 888W. Thats how much power the pack can supply, end of story. Power is energy per unit time, this means that the total energy the pack will give you is 888W * 240s = about 213kJ.

Now assume that we have it your way, and you combine the two packs and double both the capacity and the voltage output, then the pack has a capacity of 16,000mAh, and a voltage of 14.8V. This means, at this voltage, it will deliver 16A for an hour, 160A for 1/10th of an hour, or 240A for 1/15th of an hour = 4min = 240s. You would be supplying 240A @ 14.8V = 3552W over this time, which is a total energy output of of 240*3552 J = about 852 kJ - four times the energy of a single pack!

Now we just violated the first law of thermodynamics, no energy for free!

Or more generally, as far as we're concerned, energy is directly proportional to a product of the voltage, current and capacity. So if you double the number of packs, you can only double the total energy. Since voltage and current are already tied together with resistance (ohms law) the only options we have are to double the voltage or capacity of the pack. We achieve this by connection them in series or parallel respectively. To double the mah and the voltage, you would need 4 packs, and to connect them in a 2s2p configuration.