For his reviews of solar and battery technology and products, Will Prowse runs electrical tests for capacity, etc. then tears batteries apart to inspect details such as internal lead size, solder/weld quality, BMS and sensor capability, etc. He has panned a number of such as junk, and found a number of gems among the crowded field of companies making this gear. If you search for his youtube channel, you can quickly find both links to good gear at good prices as well as his reviews. He also has detailed plans for making your own systems, and changes recommended gear from time to time as he finds better options. I can recommend both his youtube channel and his book.
