Processing and storing elderberry juice
To process and store elderberry juice safely and effectively, follow these steps:
Clean and prepare the fruit: Rinse elderberries under cool running water, remove stems and leaves, and place them in a pot for juice extraction. Heat gently over medium heat to release juice, then strain through a sieve or cheesecloth. Sweeten with sugar or honey and add 1 T. lemon juice for flavor.

Sterilize jars and equipment: Wash jars and lids in hot, soapy water, and sterilize jars by boiling them in water for 10 minutes.

Fill jars: Pour the hot elderberry juice into jars, leaving about ¼ inch headspace at the top. Remove air bubbles and wipe rims with a damp cloth.

Process jars: Place filled jars in a water bath canner with at least 1 inch of water covering the tops. Process jars using a water bath canner to preserve flavor and prevent spoilage.

I think you can eliminate the sugar and just add lemon juice to each jar and water bath.