brand new backup phone out of sealed box won't charge but also over 12 months old

If the phone was never charged after purchase and sat in a box unopened for more than a year, the battery died. Lithium iON batteries when fully discharged for an extended period of time usually can't be revived and will need to be replaced. If the phone is out of warranty, you'll have to pay to have the battery replaced. It's not Apple's fault the phone wasn't ever charged during the warranty period.

Did you tried with other charger?

Apple will still troubleshoot this with you. Still contact them for assistance.

First off, you do not know if it "never worked" because you never tried it when you bought it over a year ago.

Second, maybe you should start with that BIG piece of info, "Australian consumer laws." This is a public Apple forum on Apple's US based website. How are we supposed to know you are in and bought the device in Australia? We are basing our replies on US based law which follows Apple's 1-year limited warranty.

In any case, the majority of our replies still stand. You messed up and then expect Apple to bend over backwards for you and you are upset at us for calling you out on your entitlement.

Now that we have these important details, let's look at Apple's options in Australia. Legal - Apple Products and Australian Consumer Law - Apple

Did Apple offer you their Mail-In repair option along with the option to take it to an Apple or Apple Authorized store?

That’s why Apple offers a one year limited warranty for defects. It’s not their fault you waited past that time to open the product.

If all troubleshooting is done and it still won’t turn on they cannot test the battery, so of course there will be a fee to get the battery replaced.

Apple Repair and Repair Status Check - Official Apple Support