its because of a faulty circuit...... or a cut out that use to give current to any device... can also be ur amp thats become faulty... try disconnecting it and than chek,, else get ur circuits chek..... it can be cheked by a clik sound the circuit will make when u re connect the battery terminal each time....
in my case i replaced the battery... but it was just a faulty circuit that had water in it due to rain.