Okay, I got the mini receiver pack and did some testing and here are my nonscientific results.
Remember I said nonscientific, I know some guys will argue with my measurements and calculations. lol
I charged the battery, and to test it under extreme conditions running two servos I put it into my nitro and vigorously ran the steering and throttle servos on the bench until the pack went dead. The servos began to slow at the 7 minute mark.
Since an electronic speedo is going to use much less power than a throttle servo, I'm going to extrapulate and say that in an electric sedan I would get 10 minutes of runtime from the receiver pack.
The receiver pack capacity is 160mah, based on the capacity and the 10 minutes of runtime in the receiver pack that means every 5 minute heat race using the mini receiver pack I am saving an equivalent of 80mah in my main battery pack.
Now, on my discharger, discharging a 3300mah battery pack at a rate that approximately simulates the car running on the track, 80mah = 15 seconds of runtime, which means I am saving exactly what almost everyone said I would save.
I'll be running in the Heart Of America Circuit this weekend in Kansas City and the track is big, but wide open and fast, lap times are around 12 seconds, so this weekend if it gets that close I will throw the mini receiver pack in the car. But it takes 45 minutes to charge!
So I am going to try to get by without it.