>>340707Not really a matter of "safe", but "performance".
The more cells you put into a pack/array, the more important balancing becomes to get the capacity the pack/array was designed to have.
One cell, it's obviously a non-issue.
Two... have to look at some factors (cost, complexity/size, development time if you're building a PCB) to determine if it's worth it.
Three or more? Yeah, balance that shit.