In the early to mid 1990s, I began to use lithium ion (Li-Ion) batteries. Most notably, SONY had provided me with camcorder batteries before they were commercially available. Initially, I had recommended others use lead-acid batteries or NiCad batteries, in view of the lack of general availability of Li-Ion batteries.
However, now that Li-Ion camcorder batteries are commercially available, I recommend their use. You will need a minimum of four batteries (two sets of two in series) for a constant-running 12 volt supply. You can either purchase four SONY NP-F730 batteries (cost approx. 4* $140 = $560 at large department store such as Fry's Electronics where I purchased some recently), or four NP-F530 batteries (approx. 4* $80 = $320).
These camcorder batteries have built in female mini banana connectors. Therefore, to connect to WearComp, which has historically used banana connectors (all versions of WearComp since 1985 have used banana plugs), the following cables are useful (one set for each pair of batteries):
While the choice of connectors is arbitrary, I have advocated banana connectors initially (among small groups of people) so that we can all share common batteries, chargers, etc., and also because they make field repairs simple (e.g. when wires break off while on long trips away from the workshop or lab). However, care is needed, as these connectors should be held together with gaffer's tape or the like, to prevent gradual separation in the clothing, resulting in exposed conductors. I suggest the purchase of three rolls of gaffer's tape in red, white, and black, and the use of appropriate colors to make sure that correct polarity is visible at all times.
In the next subsection, I will explain how the two pairs of batteries are connected together.