I added a battery in ‘My Components’ but it isn’t showing up as an option in the Inverter task.

When you add a battery component, you must ensure that you have checked the appropriate checkbox to set its compatibility with your custom inverter category or specific inverter

1. Create battery component 
2. Under battery rules select 'Selected inverter groups only' or 'Selected specific inverters only'
3. Click on the text to show the different inverters and select the check box under your relevant inverter group