Novak makes their smart stop modules for 2-3-4s lipos. Mike used to sell a li-saver, which automatically figured the number of cells when you plugged it in and would do a 3v per cell cutoff. Someone else makes an external lvc, just can't remember who...
I might just do it by time, I rarely use two full 5s A123 packs, and those are roughly 8 mins full out.
“The modern astrophysical concept that ascribes the sun’s energy to thermonuclear reactions deep in the solar interior is contradicted by nearly every observable aspect of the sun.” —Ralph E. Juergens