WOW - thoose are some expensive packs you got
Are you equalizing your packs before you put 500sec back into them?
A good rule is for every week not racing, charge the pack 500sec or 1000mah. If you are not going to be racing for a month or so, you might want to cycle your packs. The only downside to cycling your packs is that each cycle will take 4-6 runs off the packs life.