lighting from a 12v lead acid battery
It depends on voltage drop you want to allow.
Your total current draw is 5A.
Distance is 2x 90m.
This is table of AWG wire sizes: wiki

If you use AWG10, which has resistance 0.003 ohm/m, voltage drop is ~3V.
If you use AWG5, which has resistance 0.001 ohm/m, voltage drop is ~1V.  

So, you have to decide what voltage drop you will allow and calculate wire gauge.

UPDATE:
You have to calculate with double distance. There are actually 2 wires, one from battery to bulbs and one from bulbs to battery. Both of these wires have that mentioned voltage drop. Thanks to mkeith for pointing it out.