I want to go from gas to electric, can I use my dc battery from my starter box to field charge my lipos?

It depends on the size of your starter battery and the size of your Lipos. Just keep in mind that a little more current will be taken out of the starter battery than is put into the Lipos during charging.

For example:
If your starter battery has a capacity of 5 amps and your Lipo is 2500 ma, you will take slightly more than 2.5 amps out of your starter battery, which means if you charge the Lipo twice your starter battery will be dead. In reality, you probably won't be able to charge the Lipo more than once before the voltage of the starter battery is too low to power the charger.

other things to look at might include if the lead acid battery you are looking at using is a deep cell type, or more like a car battery. The latter do not like deep discharges, and it can ruin them quite quickly. The other thing is how many cells does your lipo have, and how many mAh is it? How many Ah is your feild/starter battery?

the simple answer basically is yes, of course with conditions.