So this is not strictly HomeKit, it is linked. I have four Eufycam 2s around my house and although the claim is 365 days of battery life, I notice that due to the use of HomeKit / HSV the battery drains quite quickly (to be fair with Eufy, they state this when you start using the Home app).
I don’t like the idea that you have to reload frequently, so I got one of these panels from Amazon. They say it doesn’t work with third-party cameras, but the connector is micro USB with an adjustable rubber seal. Since I can confirm this work, I thought it might be useful information for others.