Since this is the only battery for the EON ONE MKII, it's hard to give it a bad rating. It is leightweight, lasts for ages, and does it's job well. But there are some design decisions that JBL made that make me not love it. The connection to the speaker could be more positive... when it is plugged in, it's quite shaky and does not inspire confidence in the jostle of a crowd. There is also nothing stopping you from putting the extension tube in before the battery (a few minutes of panic ensue, because the speaker won't start) or putting the extension tube in the charger instead (they really don't weigh that much different!). It would have been nice if they'd made the connection into the speaker and charger so that the speaker and extension tube don't fit in the wrong place. Otherwise, great.