Depends on the size of your batteries, and how many cells each one has. In parallel circuits, currents are added but voltages need to match. So for example, you shouldn't put a single 4V Li cell in parallel with a single 2V Pb cell because then the Li cell will apply a net voltage of 2V to the Pb cell.

Manuel Schnabel Thanks for your information. what if we decouple each battery using a separate dc dc converter. For clear idea, please look into my other questions related to it.

Usually the elements are selected. Those, elements assembled in a group should not have very different parameters (for example, operating voltage, internal resistance). If, for example, during series connection one of the elements has a relatively high internal resistance, then it will limit the entire series, and so on. If you have access to a large number of same elements (for example, in manufacture), then it is not difficult to collect the required quantity for assembly, but with a limited quantity, this can be a problem. In the "professional case", the elements are connected in a circuit using active components to neutralize their differences, both initial and arising during the discharge process.