Checksum calculation algorithm for data dump

I have a dump of data stream where the second last byte is a checksum similar to CRC I need to be able to generate a check sum calculation algorithm for new data the first byte is the id of the device the next 4 1/2 bytes relate to the latitude and longitude position the next 3 nibles appear to relate to the battery and number of satellites and the last byte is a checksum or crc it may use a different seed polinomial depending on the device ID