The Battery Assisted Passive (or BAP) tag really got UHF Gen 2 technology going with sports timing since the tags could be placed very close to the runners skin without any degradation in read performance. The BAP derives it’s power from a patented liquid battery that kept the integrated circuit in a wake state so that more precious back-scatter energy could be used in the tags transmission rather than wasted powering up the internal circuits. The BAP was still not technically an active tag.
There were two things that killed the BAP as a viable tag for sports timing. Firstly the cost of the BAP at around $1 made it an expensive tag to use compared to the smaller and cheaper passive Gen 2 tags coming out from UPM (now Smartrac) and Alien. Secondly the passive Gen 2 tags improved greatly in read sensitivity thanks to the development of the Monza 4 (and now Monza 5) and Higgs 3 integrated circuit. Passive tags still struggle to read when directly placed on the skin but the separation needed (using a foam spacer) is a lot less these days and does not really bother either the runner or the race organizer. The company PowerID that developed the PowerT BAP went into a hiatus and no longer sells the tag. RFID Race Timing Systems was involved in the early days testing and fine tuning the PowerT but like many R&D projects, this solution turned out to be a dead end. Today the Smartrac and Alien Gen 2 tags are used in the bulk of timed events using UHF technology.