heres a link to how lnarachi and i have been powering our ad2ks since circa '02:
http://simplefuels.com/tapergeek/liion.htmthe cells are cheap if you can find the chargers
this was from the era before high-voltage li-ions were common. iwasnt into luggin lead. nowadays of course there are plenty of liion packs of varying voltage, but youre still looking at about $200 to get something with this capacity+ a charger
with good cells, it will run the ad2k alone for 7+ hrs, and with the switching power supply installed inside, feeding the v3 a regulated 6v, it will run v3+ad2k for 4ish hours
that $150 was for two complete packs (4 cells). in the field, i always used a single two-pack cell, and kept a third handy and hot-swapped it if necessary. i think the last time i bought new 2494 cell kits, they were $1 each+ shipping, maybe came out to $5 each shipped. considering they made a lot of tecras, there will probably be cells around for a few more years.