In the (distant) past I've been involved with projects that used Biotrack necklace radio tags on Red Grouse. These were very reliable and had a lifespan of around a year or more (sometimes birds from the previous year were still detectable during the new seasons fieldwork). Given the advances in battery technology and the much greater size of T.u. I would have thought they would be able to carry a device with enhanced capacity. The pulse length and rate can also be varied to extend battery life. That was back in the late 1990's though. Also Rred grouse tend to live on open hill ground rather than forest so a woodland grouse tag might benefit from extra power depending on desired detection range. However I know that some researchers using tags much more recently on Black Grouse (T. tetrix) have used similar devices in situations probably more akin to those you are likely to encounter with T.u. and have achieved up to 30 months battery life; see: https://www.researchgate.net/publication/276306561_Habitat_use_by_Black_Grouse_Tetrao_tetrix_in_a_mixed_moorland-forest_landscape_in_Scotland_and_implications_for_a_national_afforestation_strategy

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I've used the small (11g?) TW3 tags from Biotrack in 2010-2011 and the battery life was good and had several working in the field beyond 18 months. It's also used as necklace for gamebirds. Didn't have malfunctioning tags over two projects and 29 used tags but I did check them when putting them on. I lost three animals but in the end I did find the tags and they were not the issue (two were buried by a predator, another was 2km away, cut and discarded by a hunter). The only downside for me was that they were encased in epoxy and changing the battery was almost as expensive as buying new ones so not really worth reusing. 

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