From my research current 26650 batteries have even mostly lower amp limits than 18650s. I know Vamped has one they claim is 60amp but I seen a few tested in person and 2 only hit 28 and third hit 33 amps. I am sure there are a few good ones out there but guys on ecr and ecf were the ones who told me 26650 mods cannot handle loads 18650s can.
26650 batteries are more for capacity with still close to 30 amps which is what many 18650 battery users wish we had..More capacity...would be nice to have a 3000mah 30 amp in an 18650 but its not going to happen anytime soon...youll notice on 18650 batteries the higher the mah gets( to a certain degree ) the lower the amps get...The Sony VTC5 was so popular at one point because it was claimed a 30 amp battery and has 2600mah when really its a 20 amp cell that can handle 30 amps but only at a certain temperature which we cant control in a mod.
On your friends box mod using 4 18650's i can see where he can use a tremendous amount of watts (although major overkill) ...with 4 of them each battery is only seeing 1/4 of the load...so he can crank it up higher than he can possibly vape at and still not worry about the batteries pretty much.
Most that use a sigelei 150w box mods only need to use 20 amp batteries and can still be safe at low ohms because they share the load as mentioned...they can use a full 30 amps and still have headroom and not worry about it..you cant do that on a single battery mech mod....you could on a dual battery mech mod however, like i was saying.
Better to be safe than sorry, man.
Are you aware the smpl is a hybrid type mod and even more care is needed than a standard mod?
On a hybrid model, the atty makes direct contact to the batterys positive post or whatever you are using and, if you chose an improper atty you will have a big problem on your hands.
Only chose an atty with an adjustable firing pin or one that protrudes a good amount from the threads.