What "act"? Like slow turnover? How cold? How old is the battery? Have you got a volt meter? Test the battery, should be 12.7v at rest. Start the machine, voltage should be 13.4+ when running. Charge the battery, disconnected, let rest for an hour and test the voltage - should be 12.7 +. If all that is good, take it somewhere for a load test - lots of autoparts stores can/will do it for free.