By Josh Ong

Published: 07:55 PM EST (04:55 PM PST)

Research in Motion is unable to match the iPad's longer battery life with its prototype PlayBook tablets, which get just a "few hours" of battery life, according to one analyst.

Analyst Shaw Wu of Kaufman Bros. issued a note to investors Tuesday warning that engineering issues with the BlackBerry PlayBook's battery life could be the cause of delays. According to Wu, the PlayBook's "relatively poor battery life of a few hours" needs improvement. By comparison, Apple's iPad gets 10 hours of battery life and the Android-based Samsung Galaxy Tab gets 6 hours.

The battery issue could "require a bit of re-engineering," said Wu, and is "likely why RIMM pushed out its launch to the May 2011 quarter." RIM had promised a first quarter 2011 launch for the PlayBook, but left the tablet off its projected revenues for its next fiscal quarter, which ends Feb. 26.

According to Wu, these battery problems have arisen partly because "QNX wasn't originally designed for mobile environments." RIM bought QNX, which makes operating systems for everything from "cars to nuclear reactors," earlier this year.

The note also addresses several other concerns over RIM. The analyst sees good progress being made on QNX, but found that developers are "questioning the wisdom" of maintaining two operating systems, BlackBerry OS 6 and QNX. Another concern for Wu is app store monetization for the BlackBerry platform, which lacks the varied app selection that Apple offers in its App Store.

Despite these concerns, RIM's Jim Balsillie has insisted that the PlayBook is "way ahead" of the iPad. Co-CEO Mike Lazaridis recently said in an interview that the PlayBook OS is will lead RIM into the "next decade of mobile computing."

Wu maintained his "hold" rating for RIM, keeping the stock's price target at $60. RIM stock closed at $58.02 on Tuesday.

Wu also emphasized his position that the iPad will continue to dominate the tablet market. "As we have said before, we are not convinced that tablets outside of the iPad will see high volume success," he wrote in the note.

Though "public expectations" project between 1 million to 8 million PlayBook units sold in 2011, Wu has a conservative estimate of just 700,000 PlayBooks sold next year.

700,000 PlayBooks would likely be a small fraction of the number of iPads sold by Apple in 2011. Apple announced in May that it had sold 1 million iPads in just 28 days from launch. During Apple's most recent quarter, the iPad maker sold 4.19 million units of the popular tablet device.

A new report from DigiTimes suggests that Apple will produce about 40 million iPads next year, though an earlier report had suggested Apple may produce as many as 6 million second-generation iPads per month.