Similarly, batteries, for an example, wired in parallel will give you more power for less capacity, while batteries wired in series gives you more capacity but less power.

You have no idea how batteries or electronics work. Adding in parallel increases capacity and maximum current and maximum power. Adding in series increases emf (volts) and maximum power and capacity. Adding extra batteries almost always increases capacity in some way. The actual duration is as much about load as capacity.

If your load is something like a resistor then adding batteries in parallel will increase duration since current draw and power output stay the same and capacity has doubled.

If your wire in series then current draw will double and power draw will quadruple because the potential difference (volts) has doubled. This follows I = V / R and P = VI. This also means the duration is halved because the power drain is 4x but the capacity is only 2x. Make sense?

I = Current

V= Potential difference (p.d) / electromotive force (e.m.f) measured in volts

R = load resistance

If something supplies power you call it's voltage electromotive force, if it uses power then it's called potential difference. Why is it this way? No idea

Please note I am not factoring in internal resistance and some other factors here because that makes things way more complicated.

Also you can measure battery capacity in two ways: amp hours and watt hours. Only one actually tells you the total energy stored, which is watt hours. To work out watt hours from amp hours you need to multiply it by the nominal imf (volts) of the battery.