In general batching is the process of measuring and combining the ingredients of concrete (cement, water, sand, aggregates)…as per the mix design. The last part is important, if you are an Engineer then you will have to do a concrete mix design to know the quantity required for each element of concrete…so basically, you will say “for C-30 concrete member we need 50kg of cement per meter cube of the member or 20kg of aggregate per meter cube…etc this is the mix design.

Now the batching( measuring and mixing) could be done in two ways like you said.

is the professional one, which is always recommended. Basically, you measure each quantity by mass (using a large weigh equipment) and batch the components in a controlled environment.

concrete plant

You see this type of batching in large concrete batching plants which have large equipments. That is weight batching. In volume batching, the mass of each component will not be measured prior to batching, instead there are these fabricated boxes(mostly wooden) which are measured in volume to contain the concrete components.

So basically, the entire mix design is changed, now you say “5meter cube of cement per meter cube of concrete”. Remember the boxes, their volume is known so you now the volume of the component that is in that box. Anyway, this method is very archaic, its old and very inaccurate…so most consultants dont allow this method on site.