Can i use car gps as personal gps ?

yes you can. because you arent moving that fast the accuracy would be much better and most car GPS systems have a battery and even a suspend mode to save power.
it might not give very good graphical data and you should try to get one that can be upgraded using a computer or through downloads you put on a SD card or something.
but, it will work. Just make sure to charge it up to full before you leave, and use its sleep mode if it has one.