Investors are picking winners in the energy storage sector, sending stocks swinging by double-digit percentages over the last week.

Energy storage and battery tech stocks are largely drifting higher on light volume today, with Menomonee Falls, Wisconsin-based ZBB Energy (AMEX: ZBB - News) leading the way, up 5.5%. Over-the-counter listed Axion Power (OTC: AXPW - News) is also a top performer, up by 3% after reporting a massive spike in third-quarter sales. The company brought in $963,000 in revenue during the three months ended September 30, up from less than $150,000 during the same period of 2008. Excluding hefty non-cash losses related to derivative pricing and preferred stock conversion, Axion lost -$1.9 million in the third quarter compared -$2.2 million last year.

Meanwhile, A123 Systems (NASDAQ: AONE - News) is slipping by -5% today after Goldman Sachs said the Street is already factoring in good news. The analyst rated A123 Neutral with a $14 price target. Buffett's bet on BYD (OTC: BYDDF - News) is also in negative territory, though Berkshire Hathaway (NYSE: BRK-A - News, BRK-B - News) is still up significantly on its October 2008 investment.

As a whole, the Energy Storage and Battery Technology Stocks Index is ahead by 1.6% today. It is currently lagging the S&P 500 by -14.5% over the last month.

Hong Kong Highpower (NYSE: HPJ - News) is the sector's biggest winner over the last five sessions, up by more than 20%. The company doubled the single EPS estimate in the third quarter last week.

Domestic players Ener1 (NASDAQ: HEV - News) and Advanced Battery Technologies (NASDAQ: ABAT - News) haven't fared as well in the last week, both slipping by more than -4%. A123 remains the worst performer for the period, down by -14%.

As of this writing, the Energy Storage and Battery Technology Stocks Index is one of the five worst-performing tickerspy Indexes over the last month. A look at the Index's performance chart versus the S&P 500 shows the sector erased gains from its latest run, but throughout 2009 buying on the dips has rewarded investors.

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