Probably the biggest risk is over discharging one of the packs. It's likely the real capacities are different, especially if the age and cycle history of the 2 packs are different.

At the very least be very careful with run time, and checking the voltage of the packs.

Note checking them while stopped is different than the LVC setting, which is under load. I would strongly suggest not going below 7.4V per pack at rest.