What are the voltages of the 2 packs and what voltage can your receiver handle? remember that the peak voltage of each lipo cell is 4.2V not 3.7, 3.7 is the nominal voltage so a 1cell pack has a peak voltage of 4.2v, 2cell=8.4, 3cell=12.6V

depending on the amp draw of your servos you also need to know the C rating of the pack. The amp draw can be calculated by taking the mAh times the C rating and then divide that by 1,000

If the 1600mAh pack has a 20C rating then it can put out 32 amps.

the one last thing that you have to do if the lipo will work is not over discharge it. they sell voltage cutoffs that you can use for extra safety but as long as you check your voltage every once in a while on the first few runs you can see how long you can run with that pack. the maximum discharge for a lipo should be 3.2v per cell.