The Ego battery packs and technology is some of the best stuff on the market. Sometimes there is an electronic glitch. 3 year warranty on the batteries so no need to worry.
The fact that a battery failed is no indication of low quality. Just as my 6 batteries that have been operating for several years are no indication of high quality. Just a very small sample size that says very little. Unfortunately it means everything to the person that owns that small sample size.
Give Ego a chance - they have high quality stuff and stand behind their products and warranties.