Me, again. After a lot of reading and thinking, I'm leaning toward getting a replaceable battery mod as well, because I hate the idea of being unable to vape while the Kroma-A is charging and am a little worried about pass-through vaping. I'm leaning toward the Pico 25. For batteries, I'm considering either the Sony 18650 VTC5a High Drain 35a continuous battery (2600mah) or the Samsung High Drain INR18650-25R 20A (2500mah). For charger, the Xtar VP2. With another Zenith tank and extra coils, this is going to bring my total expenditure up to almost $150 for the two setups. I wish I hadn't jumped the gun on the Kroma-A and just gone for the Pico to begin with.
I'm not sure the Pico 25 is a wise choice for the Zenith tank. There's not much room for the tank because of the battery knob taking up so much space. It may work, but it will probably be a tight fit. The Ello tank is allegedly 25mm and it fits. I've seen the Zenith described as a 23, 24, and 25mm depending upon the vendor.
The Xtar VP charger is a great choice. I have the VP4 and love it.
Batteries you've chosen are good, however for future reference you might get longer use with a lower amp battery with more mAh, depending upon what wattage setting you end up using.
WATTAGE PER SINGLE BATTERY on REGULATED MOD:
(Total wattage doubles using 2 batteries; Triples using 3 batteries.)
Up to 45W:
Samsung 18650 30Q, 3000 mah 15 amp CDR
Sony 18650VTC6 3000mAh 15 amp CDR
Up to 60W:
LG 18650HG2 3000mah 20 amp CDR
LG 18650HE4 2500 mah 20 amp CDR
Samsung 18650-25R, 2500 mah 20 amp CDR
Sanyo UR18650NSX, 2500 mah 20 amp CDR
Sony 18650VTC5, 2600 mah 20 amp CDR
Sony 18650VTC4, 2100 mah 23 amp CDR
Up to 75W:
LG 18650 HD4 2100 mah 25 amp CDR
LG 18650 HD2 2000 mah 25 amp CDR
Samsung 18650-24S, 2500 mah 25 amp CDR
Sony 18650VTC5A, 2500 mah 25 amp CDR
Up to 90W:
LG18650HB6 1500mah 30 amp CDR
LG18650HB2 1500mAh 30 amp CDR
LG18650HB4 1500mAh 30 amp CDR
Samsung 18650-20S 2000mah 30 amp CDR