Do you have any idea how to do it within a batch-file? somehow with ping-commands?

Should be easy enough if you have the empeg on a fixed IP.
I'm not very good at .bat files (assuming you use Windows) - instead I'd use Perl, capture the output of a packet count limited ping command (see below) and grep it for stuff indicating that the machine is available (like "64 bytes") and if present go ahead and ftp the routes. If you want to run this on your computer in the morning before going out to the car you could have it loop the ping+check along with a sleep, until it finds the empeg, then ftp and when done, exit.

Machine available:

tempsch:~$ ping -c 3 192.168.1.31
PING 192.168.1.31 (192.168.1.31): 56 data bytes
64 bytes from 192.168.1.31: icmp_seq=0 ttl=128 time=0.2 ms
64 bytes from 192.168.1.31: icmp_seq=1 ttl=128 time=0.2 ms
64 bytes from 192.168.1.31: icmp_seq=2 ttl=128 time=0.2 ms

--- 192.168.1.31 ping statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max = 0.2/0.2/0.2 ms


Machine unavailable:

tempsch:~$ ping -c 3 192.168.1.15
PING 192.168.1.15 (192.168.1.15): 56 data bytes

--- 192.168.1.15 ping statistics ---
3 packets transmitted, 0 packets received, 100% packet loss


/Michael