public function getBalance(){

        $ch = curl_init( $this->balance_address );
        curl_setopt($ch, CURLOPT_POST, 1);
        curl_setopt($ch, CURLOPT_POSTFIELDS, 'username=' . urlencode( $this->username ) . '&password=' . urlencode( $this->password ) . '&currency=LTL' );
        $output = curl_exec($ch);
        curl_close($ch);

        $data = simplexml_load_string( $output );

        return $data;
    }