Here's a very small LVC that you can use:
http://www.dimensionengineering.com/LipoShield.htm It's one of the cheapest that I know of. You may want two of these, one for each battery. You would hook them in series together (one's RX cable to the other's RX cable input).
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