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(v) Turn on the mains supply at the distribution board only if the unit passes all the above tests. Note: If the mains is disconnected and the battery is almost depleted the unit will beep every 40 seconds for at least 72 hours. This is to remind you to re-connect the mains supply. The unit will operate from the mains alone, even with a fully depleted or a defective battery, though it may not give sufficient warning of fire if the mains supply is disconnected for any reason. If there are any pro