I could do the same with a old ASIc miner on ETH and BTC but I believe you need a stable grid power, just plug and ready to mine for a very long time without looking back, this is the way but unfortunately the grid power in my country sucks so much
Why is that so ? And if so, what country do you currently live in ? so it can be very difficult to get to the network and it can take so long to mine BTC as well as ETH.
Because if the tools and equipment can be very adequate, I don't think it will be too complicated to make mining on both.