NEW YORK — Combined sales among TWICE’s Top 25 car electronics retailers fell in 2009 by 10.6 percent to $5.12 billion, and only eight retailers on this year’s Top 25 list posted gains.

Double-digit declines were the norm for dealers making the 2009 list, yet as a group, the top 25 dealers easily outperformed the industry, based on the Consumer Electronics Association’s estimated 42.6 percent decline in 2009 factory-level aftermarket car electronics sales. The decline was driven mostly by a 58 percent drop in portable navigation device sales.

Best Buy, Walmart and RadioShack maintained their respective positions as the nation’s first-, second- and third-largest retailers of car electronics even though each suffered double-digit percentage-sales declines.

TWICE’s research also found that the mass merchant, consumer- direct, and 12-volt specialty channels posted slight dollar-share gains among the Top 25 retailers, while electronics and electronics/ appliance dealers post slight dollar-share declines.