n1ckelov:
Damn, just realized that I need 12V 2A to output from battery not from solar cells :-X
The 3x 18650 will do that for a short time. But charging them in series as a battery pack is far more complicated than charging them in parallel. Then charging an series-parallel 18650 (or any Li-Ion pack) is even more complicated.
How long do you need 2A? 10 seconds, 10 minutes, 10 hours, 10 days?