EHFAI

I don't know if break-in is good or irrelevant, seems like it's a good idea.I break-in new packs on a test stand where I can monitor individual cell volts and overall output. Stand is equipped with a low cost motor that can handle 30A for 6 min. Packs are allowed to cool completely before charging after each run and the process is repeated 5X. Using brand name packs I've not experienced any early failures - but it may not be absolutely necessary.

A much more important practice as packs age is to check the individual cell volts at the beginning of charge. The balance connectors on packs (and any extensions) deteriorate with use and can provide false info to the balancing circuits of the charger. Of course, that means the balancing attempts of the charging system will be in error, possible over / under charging some cells. Kinda defeats the purpose of balancing! It's very important to determine if errant cell voltage is correct or a connector problem before "mis-charging" the pack! Sometimes cleaning the connectors will fix the issue, sometimes "tightening" the connector is needed, and frequently several strands of the balance lead are broken at the connector resulting in big voltage drop when balancing current is flowing.A little observance / maintenance here will result in longer batt life.