Shares of A123 Systems Inc. declined again on Thursday. A Wunderlich analyst is saying that the Waltham company’s new technology won’t be enough to keep it afloat for long. A123, which makes batteries for electric cars, said its Nanophosphate EXT, which is calls a better lithium-ion technology, can handle “extreme temperatures without requiring thermal management.” The shares soared over 50 percent on Tuesday after the announcement, but then began retreating. “A buy or bye-bye for A123 Systems?” asked The Motley Fool.