The Enphase AC Battery is a residential energy storage system, integrating solar and storage as a part of a complete Enphase home energy solution.
When it comes down to the specs, there isn't a difference between the two Enphase batteries, the Enphase AC Battery and Enphase IQ Battery. Both have equivalent output data, have Lithium Iron Phosphate battery chemistry with a capacity of 1.2kW / 48.5 Ah, and the same dimensions and other features. You can view the datasheets for yourself to compare:
However, the Enphase AC Battery is integrated with the Enphase S280 Microinverter, part number S280-ACB-LL-US, while the Enphase IQ Battery is integrated with the Enphase IQ 6+ Microinverter, part number IQ6PLUS-ACB-LL.
To see the difference between the Enphase IQ 6+ vs S280 view the following article: Enphase S280 vs IQ6+ Comparison
Note that the IQ Battery is not yet available for purchase.