As long as both packs see the same type of usage, are drained to approx the same LVC, and are cycled the same number of times, it's ok. If it were me, when you get ready to use them together again, balance them as a single pack until perfect, then charge like that.
Or, balance them now so they are exactly the same, and then run them in parallel. Lots of runtime and you can be sure you'll never come close to the C rating unless you are shooting for 150mph in your Slash.
