Non-isolated DC/DC Converters are the lowest cost method to draw 12 V power off the entire pack and maximize not only the life of the batteries, but also the range of the vehicle. Some battery manufactures will not warranty batteries for early failure unless 12 V loads are powered by a true DC/DC converter.
There several models available:
16 Amps constant, 20 amps intermittent
With input& output fuses in harness, PN 20430-B
Without input and output fuses in harness (customer to supply fused terminal blocks), PN 20430