My suggestion:

## 1. Use fastq-dump on each of the files, e.g. parallelized with GNU parallel:
ls *.sra | parallel "fastq-dump --gzip --split-3 {}"

## 2. Check files with fastqc:
ls *.fastq.gz | parallel "fastqc {}"

## 3. If metrics are ok, combine them:
cat SRR*_1.fastq.gz > merged_1.fastq.gz
cat SRR*_2.fastq.gz > merged_2.fastq.gz

## 4. (optional): Trim with skewer for adapters and low-quality bases/reads:
skewer -n -q 25 -Q 25 -m pe merged_1.fastq.gz merged_2.fastq.gz

## 5. Proceed with your downstream alignment or assembly