That’s an interesting question (about battery consumption and aggressive reconnect attempts). One of the Android devs could answer this more completely I’m sure, but I remember when I used to play a few games on my phone, there would often be single domains being blocked over 50 times a minute, and I didn’t notice a decrease in battery life. It’s the software that is aggressively initiating repeated connection attempts which would be responsible for any potential change in battery life too, not Blokada.
HBlock is a trustworthy project, and quite comprehensive, so I would also recommend not using too many additional lists if you’re using HBlock. A good rule of thumb is to have no more than 3 or 4 lists enabled at any time, and to choose ones which fit your needs and habits. This reminds me to mention that it’s memory consumption one should keep an eye on when using a Local VPN, DNS-based blocking solution like Blokada. While I’ve never noticed a big hit on battery life, I have noticed big hits on available memory when using a lot of comprehensive lists at once. This would apply to even the most stripped down Local VPN, DNS-based blocking applications. I’m of course partial to my own list, so I only use that, but if I was using HBlock, I’d probably only combine it with one or two other, smaller lists at most.
There’s very comprehensive multipurpose lists like HBlock, smaller, more focused lists like Dan Pollock’s, URLHaus, and The Block List Project. Then there are lists which attempt to occupy a middle ground, like mine, and the default OISD light list. Some people might need or want to block over 500,000 domains, and some people are OK with 50,000, or 100,000. It all depends on what you wish to accomplish, and the available resources on your device.
DNS resolvers also play a role here too. For instance, if you were using OpenDNS or Quad9 (both of which are quite efficient at blocking malware servers), then selecting lists which mostly focus on advertising and tracking would be the sensible choice. On the other hand, when using a non-filtering resolver like Cloudflare, you’d likely want lists that have you covered in both regards. Then you have the other end of the spectrum, with resolvers like AdGuard, where it would be ideal to use lists that include a good amount of entries to protect against malware and suspicious domains. I’m getting out of scope here, so I’ll stop myself.
TLDR: You don’t have much to be concerned about from Blokada when it comes to a domain being repeatedly blocked. On the contrary, look at the app which is ceaselessly initiating those requests. Also, choose your block lists depending on what works best for your device, and for you.