Unfortunately there are a log of blogs out there linking to a lot of products that claim to double your DS4's battery life. These are unfortunately all BS.
They are just mis labeled and falsely sold DS3 batteries, which are usually only 800mAh which is even less than the DS4 OEM battery which is 1000mAh.
The only way to guarantee a longer battery life on your controller is to get a rock solid no BS battery from a battery website or hobby site. In the video below I outline what I believe is the best pack that you are going to find out there that fits with minimal modifications and improves your battery life.