I just bought the standard combo action 4. And noticed it came with a lens cap with no glass on it , just a open hole. Might be a stupid question,  but what is it used for?
Oh also are there any good 3rd party batteries? Or best to just buy the ones from DJI?

Hi, there. Thank you for reaching out. May I confirm if you're referring to the Osmo Action Lens Hood? If so, this accessory you mentioned is a lens hood recommended for use in complex lighting situations, such as backlighting, to capture cleaner images.

Use Tips for the Lens Hood
1. Osmo Action 4 is not waterproof when used with the Osmo Action lens hood. Please avoid using it in high humidity or underwater environments.
2. When using the Osmo Action 4 camera with a lens hood, be careful to avoid scratching the lens, as it is exposed. Please use it with caution and remember to replace the lens hood with the lens cover after shooting.

Furthermore, it's recommended to use genuine DJI products and accessories as third-party items aren't tested and may harm your DJI Product. Thank you for your understanding.

You may refer to the image below. Should you have further concerns, please don't hesitate to reach us.

DJI Gamora Posted at 1-20 22:31
Hi, there. Thank you for reaching out. May I confirm if you're referring to the Osmo Action Lens Hood? If so, this accessory you mentioned is a lens hood recommended for use in complex lighting situations, such as backlighting, to capture cleaner images.

Use Tips for the Lens Hood

Can you buy the lens hood separately

djiuser_yrZubY443H2s Posted at 4-26 10:42
Can you buy the lens hood separately

Hi, djiuser_yrZubY443H2s. Thank you for reaching out. Yes, you may purchase it here.