For the fourth time in a row, the iPhone has come in first in J.D. Power and Associates’ semi-annual smartphone customer satisfaction survey with a score of 800 out of 1,000 — well ahead of its competitors.

If it weren’t for the iPhone’s battery life — much improved on the iPhone 4 but still all-too-brief on older models — the device would have scored five perfect gold circles across the board (see below).

LG, with a score of 731, was the winner in the traditional handset category, also for the fourth consecutive time.

Satisfaction with their handsets may be one reason customers seem to be hanging on to them longer — an average of 20.5 months, up from 17.3 months in 1999, according to the news release issued Thursday. But the report suggests that price consciousness in the economic downturn may be a bigger factor.

“Typically, when upgrading to a new cell phone, there’s the added expense of either subscribing to a more expensive service plan and/or incurring termination fees when switching service providers,” said Kirk Parsons, J.D. Power’s senior director of wireless services. “Today, consumers are really watching their wallets, and any added discretionary expenses are being considered more thoughtfully than in the past.”

Below: The smartphone ratings.

[Follow Philip Elmer-DeWitt on Twitter @philiped]