The TX being down to 9.0 would be asking to crash. The drop from 9.5 to 9.0 (and below is very fast. Do not take off if the battery reads 9.6 or below on the TX. (I tend to quit before it reads 10.0...)

I also don't take off if my RX pack is below 4.9 v.

I may be a bit on the conservative side with the votages... but I don't lose planes to dead batteries.

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The time you can get with any given mah rating pack is dependant on too many factors to say you can depend on timing to say you are safe.

Depending on how I fly one model... I can get anywhere from one 20 min flight to four 30 min flights from one charge of a 700 mah pack. (obviously I moved to 1800 mah packs for that model to ensure I'd be safe for at least 2 flights.)

The average TX is gong to be able to operate 2 hours on a 700 mah pack. It is uncommon for the TX to run out of power before the RX. (unless the guy forgot to charge the TX...[&:])