The Australian National Dictionary Centre (Australian National University, Canberra, Australian Capital Territory) writes that, in Australian English, the noun battler designates a person who struggles for a livelihood, and who displays great determination in so doing.

It is now the phrase little Aussie battler that is often used to characterise such a person.

This phrase occurs, for example, in ‘Forgotten’ Williams hits the target, a correspondence from Melbourne, Victoria, Australia, by Mark Hodgkinson, published in The Sunday Telegraph (London, England) of Sunday 24^th January 2010:

IF VENUS Williams had the full attention of the locals on the middle Saturday of the Australian Open, it was only because her opponent was ‘a little Aussie battler’. That’s Australian for ‘a member of tennis’s lumpen proletariat hoping to catch a seed on an off day’, in this case a wild card ranked 980 in the world who has been known to shop for her match-day tank-tops at Target, the cheap and cheerful chain store. If it had not been for Casey Dellacqua, and it’s not often that you say that, Venus would have continued to be the Forgotten Sister of Melbourne Park.

The texts containing the earliest occurrences of little Aussie battler that I have found indicate that this phrase was originally applied to the Australian television host, radio presenter and singer Ernest William Sigley (1938-2021).

The earliest occurrences of the phrase little Aussie battler that I have found are as follows, in chronological order:

1-: From The Bulletin (Sydney, New South Wales, Australia) of Saturday 2^nd March 1974:

TELEVISION
The star of every public bar
By DENIS O’BRIEN

ERNIE Sigley now comes at us twice a week on the National Nine Network as “the little Aussie battler,” a Channel 9 promotional slogan which says as much about the truth of Sigley’s position in the Tonight Show hot seat as it seeks to coat him with the endearing qualities of the cheeky, cheerful and indomitable underdog.
[…]
He is less a little Aussie battler than a confidently cocky and amusingly vulgar little bloke—one of the boys, the star of every public bar.
[…]
ABC TELEVISION is about to show the results of its study of a little Aussie battler of an entirely different sort. Billy and Percy, the latest dramatised documentary to come from John Power […] is due to be screened in New South Wales on March 6 and later in other States.
The Billy of the title is Billy Hughes (Prime Minister from 1915 to 1923); Percy is Percy Deane, Hughes’ private secretary through most of the turbulent years.

2-: From a television review, by Lorraine de Selle, published in The Australian Women’s Weekly (Sydney, New South Wales, Australia) of Wednesday 19^th June 1974:

KNOWN far and wide as “the little Aussie battler,” Ernie Sigley battles on regardless with his undoubted talent and the team of regulars on his entertaining show.

3-: From the following advertisement, published in The Canberra Times (Canberra, Australian Capital Territory, Australia) of Wednesday 22^nd October 1975:

SHOCK HORROR

Words cannot adequately describe the savage price carnage

WROUGHT

by the little Aussie battlers who first brought you thirteen to the dozen.

PROBE

Farmer Bros have probed the soft underbelly of their opposition and exposed it for what it is—flabby profiteering.
Farmer Bros share these advantages of bulk back in June were excessive. Now they are showing you just how you are being ripped off by those liquor sellers who don’t cut prices like Farmer Bros.

WAR

For instance as part of their war on prices, Farmer Bros this week are selling Hardy’s 4,54 litre wine casks for $4.99. They can afford to do so because when they buy Hardy’s wines in 40 case lots they get a discount of five per cent. Farmer Brow [sic] share these advantages of bulk buying with their customers. When they buy better, you buy better. When their chain store rivals buy, often in far larger quantities and with larger discounts, the benefits don’t show in your pocket.

4-: From a theatrical review, by Brian Hoad, published in The Bulletin (Sydney, New South Wales, Australia) of Saturday 27^th September 1975:

Another new play called Sonny, by a young South Australian, Ian McGrath, seemed to crop up at the Ensemble Theatre as fresh as a daisy. It concerns the journey from conception to maturity of a little Aussie battler whose most difficult lesson is to learn not to battle so hard. Both life and death, suggests the play, need to be taken more lightly.

5-: From A new force on the hustings, published in The Canberra Times (Canberra, Australian Capital Territory, Australia) of Thursday 27^th November 1975:

IN an attempt to introduce some irrationality to the general election and to give the voters an irrational alternative to the major parties, a young Canberra man and some colleagues are hoping to form the Little Aussie Battlers’ Liberation (LAB LIB) Party.