Re-analysis of multiple scRNAseq data as a combined new one

Hi all,
There are so many regions in brain.The cortex itself is of many types.I found many single cell RNA seq studies which focus on different regions eg-

gse … somatosensory cortex dropseq year 2015

gse….. primary visual cortex smartseq 2017

gse….. cortex whole 10x 2019

gse…. motor cortex 10x 2020

gse ….. white and gray matter in cortex smartseq2 2021

Can I combine them all to check gene expression of geneX in the cortex showing relative expression in the above regions.Is it a possible insilico study?

Will there not be a lot of batch effect?If so how can it be avoided?

Will I have to start from gene count or download SRR so that all different scrnaseq studies are quality controlled in the same manner.

Kindly guide.

Also, suggestions of combining various studies to answer the relative abundance of gene in various tissues are also invited.