There is also the Li-saver, which causes the motor to stutter when the voltage gets low:
http://flydma.com/lithium/lithium.asp?path1=lithium
SH Z-Car, Custom Crawler, 8s Savage,
12s XTM XLB 1/7 buggy,
4wd 4-link rear/IFS Pro4 truck,
Custom Hyper 10 Short Course,
Belt-Drive Mammoth ST 1/8 truggy, 4s 17.5 MM Pro HPI Blitz