does single vs dual battery matter with regards to amps?
Depends on the mod design and configuration.
Mech mod, single battery the battery must be able to handle all the load at a full battery charge, 4.2v. So to see your requirements, you would use in a calculator for Ohm's Law, 4.2v and your coil resistance, personally I suggest for any mech mod you run Sony VTC3, Sony VTC4, or LG HB6 30amp batteries.
Mech Box mod, parallel dual battery configuration, here in this config your base voltage stays the same, 4.2v, yet load is equally distributed across both batteries, Samsung 25R for instance, 20amp CDR, 2500mah per single cell, in a parallel config it becomes 4.2v, 5000mah, 40amp CDR you can do.
Mech Box Mod, series dual battery configuration, here voltage is doubled, yet Mah and Amp CDR stay the same as a single cell, again Samsung 25R again, 2x in series, voltage is 8.4v, 2500mah, 20amp CDR in this configuration.
Regulated mods, play a little differently, max CDR is at the lowest charge state of a battery instead of the highest, most regulated mods stop firing at about 3.2v to 3.6v. So you take your max wattage, divide that by lowest battery state, gives your max CDR the mod will ever need.
Sigelei 150watt for example, runs in series, see above, we double battery voltage here, so, 150watts/6.4volts (3.2v X2)=ending potential max CDR you will need, which is 23.4375amps, only batteries that can handle that are Sony VTC3, Sony VTC4, and LG HB6 30amps
Sigelei 100watt, runs in series like its bigger brother, 100watts/6.4=15.625amps, any battery 15amps or above will work in this application LG HG2, Samsung 25R, Samsung 30Q, Any Sony VTC Series, LG HB6, LG HE2/HE4
iStick100watt, parallel battery config, mah and amp load are shared between batteries while they provide 4.2v, so 100watts/3.2v=31.25amps no battery can handle that, but if the lowest the iStick will fire at is 3.4v, 100watt/3.4=29.412amps, again Sony VTC3/VTC4, LG HB6 for this application
Sigelei 75watt, single battery, 75watts/3.2v=23.4375amps, at 3.4volts 100/3.4=22.06amps, here you can fiddle and wiggle a bit, LG HE2/HE4, Samsung 25R, Sony VTC5, MNKE (all 20amp CDR), Sony VTC3/VTC4, and LG HB6 can be used, just depends on how safely you want to skirt the boundaries
A lot of people are surprised by just how much math is involved in vaping, learning the variables of your equipment goes a long way when it comes to safety.
Hope that explained things a bit better for you.