Globalsecurity says a battery is "equivalent" to a Company or somesuch. How many guns in a battery? Just curious, because I do not have that number, and if I did, I probably would not have the number for a Australian artillery battery.

A battery is usually 6-8 guns. Who exactly is Australia worried about?

This is not a simple question to answer. If you consider a "typical" to&e, you would have three (3) battalions of infantry and one (1) battalion of artillery in a infantry brigade. (Assumption being that there are three (3) batteries of artillery in that arty bn, the fourth arty "battery", even an "ad-hoc" one, being absorbed into the Brigade HQ). Going by that, the answer would be NO, not enough artillery. But life isn't that simple. As the previous posts pointed out, there is the issue of what the mission is and who the potential enemy is. And on a much larger scale, just like those of us who have to balance a checkbook when there isn't enough money, the issue of what the nation can afford raises its ugly head. Artillery battalions are much more expensive to maintain than infantry battalions. Not to mention all the support units they need to be able to function. So while someone in the Australian military probably asked for a artillery battalion per Reserve brigade, cost probably dicated that they got no more than a battery. And when conflict breaks out, things get really interesting, because now the creative juices are flowing and people are more willing to take risks. So that same Artillery battery could grow into a "battalion", if they could get enough artillery pieces, even obsolete ones. Or the unit is given large mortars in place of non-existent artillery pieces, since mortars are quite a bit cheaper to produce. Or any other variation you can think of, since I'm sure someone has tried it during one war or another. So the real answer to your question may be that its all that they could afford.

I have a question. Their role is to protect airstrips by patrolling. OK. Is there any consideration of CAS from these airstrips ?

The airstrips may be interdicted...mines and stuff dropping onto the airstrip. Or they may be hit by those run-way breaker things like Durandal. That and maybe weather conditions. Arty is all-weather fire support.