it will last 7 hours, you could get a higher capacity battery (i.e. bigger number of Ah)
you could use 2 batteries and swap between them, use one and re-charge over night, add a switch in between the battery and router so you can turn it off when not in use, or use one of the options in post #11 on this thread.

Hope this helps,
Mike

What battery do you recommend? I would need one that lasts a couple of days at least

http://www.maplin.co.uk/Module.aspx?...0acid&doy=30m3 this 12V 12Ah will last 12 hours with your router

http://www.maplin.co.uk/Module.aspx?...0acid&doy=30m3 the 12V 65Ah will last 65 hours but is £69.98

it probably would be cheaper to get a socket depending how the socket was done