The other answer already talked about scheduling priority, and it surely answers to exact question. That said I think your word prioritize is been used a bit unusual way and you actually mean how can make the batch download not to effect other networking. Answer to that question is traffic controlling.
Here is an example traffic shaping script (from funtoo.org).
modemif=eth4
iptables -t mangle -A POSTROUTING -o $modemif -p tcp -m tos --tos Minimize-Delay -j CLASSIFY --set-class 1:10
iptables -t mangle -A POSTROUTING -o $modemif -p tcp --dport 53 -j CLASSIFY --set-class 1:10
iptables -t mangle -A POSTROUTING -o $modemif -p tcp --dport 80 -j CLASSIFY --set-class 1:10
iptables -t mangle -A POSTROUTING -o $modemif -p tcp --dport 443 -j CLASSIFY --set-class 1:10
tc qdisc add dev $modemif root handle 1: htb default 12
tc class add dev $modemif parent 1: classid 1:1 htb rate 1500kbit ceil 1500kbit burst 10k
tc class add dev $modemif parent 1:1 classid 1:10 htb rate 700kbit ceil 1500kbit prio 1 burst 10k
tc class add dev $modemif parent 1:1 classid 1:12 htb rate 800kbit ceil 800kbit prio 2
tc filter add dev $modemif protocol ip parent 1:0 prio 1 u32 match ip protocol 0x11 0xff flowid 1:10
tc qdisc add dev $modemif parent 1:10 handle 20: sfq perturb 10
tc qdisc add dev $modemif parent 1:12 handle 30: sfq perturb 10
What you need to do is to find out criteria[1] of what sort of traffic you want to de-prioritize by granting it only limited bandwidth. These setting should probably live somewhere in your system start up configurations instead of the script you run.
[1] an address where you download from, or protocol, cgroups which processes are downloading, etc.
See also
How to priotize packets using tc and cgroups