When do you replace your tranceiver batteries?

The F1 is indeed still sold, and probably will always be sold to meet the needs of "traditionalists" as well as cheapskates (or at least those cheapskates who are incapable of buying anything below MSRP).
My take:
www.wildsnow.com/1476/avalanche-beacon-review-intro/
"Yes, once upon a time all we had were analog-only single-antenna models such as the F1, VS 2000, Optifinder, etcettera. And I’ll believe that certain grizzled vets out there (Lou?) are capable with their old beacons. But as one internet poster commented, “I don’t trust anyone with an older-style beacon unless he has a gray beard.” Same here."

  I hate to throw something away that I know works. 
Alan

Riding the buggy is quaint but I'm going to the ski hill with the guy with a car.

Frequency drift not currently an issue with these units.  

Did you actually test them for drift with something like a Pieps DSP?

Every analog beacon I've tested with my DSP seems to have at least some drift, often substantial. Don't see anywhere near as much with any digitals.

Plus the other reasons that I linked to.

They were picked up well and searched well.  I hate to throw something away that I know works.

Are you suggesting the CAA are wrong? And that you know better? Because that'd be either really ballsy or just plain stu...

...I put my ~70% AAA's into my LED headlamps... That is my standard use for bEacon batteries.

I’ve tested many old F1 beacons (the ones with the pale blue housing) from a larger loaner fleet that had only very minor drift, still well within the spec, which is also typical of any modern directional beacon.
However, I’ve also noticed that many of those F1 units that tested out okay one year had then drifted beyond the spec by the following year. So just b/c an old F1 is fine now is no reassurance for the following season.

The CAA makes some good points, but would be more helpful if they more clearly separated out searching vs. being found. Also, some of their points relate only to old F1 beacons, which although they probably comprise the majority of single-antenna beacons still in use, have characteristics that are not shared by all such designs. (Plus I’m pretty sure that this statement is not necessarily true: “That means if two people are buried close together, the one with the digital beacon is likely to be isolated first.”)

But back to the main point, just b/c an old F1 or some other single-antenna design seems to work well in some unspecifed practice regimen compared to some other unspecified model(s) with practice partner(s) of unspecified proficiency, all of that is not very reassuring at all. I mean, with proper training and a current design, you might find yourself much better at beacon searching, but you probably wouldn’t know that based on this kind of experience so far. (And also, although I’m trying my best to be polite, worrying about battery strength and type in such detail while sticking with such an old beacon design just seems really backwards.)

What a great topic with such an amazing range of opinions.  My personal experiences and observations with most every beacon on the market, using them for avalanche class exercises, day trips and mult-day trips , has shown me the following: 1) if your beacon performs poorly in receive depending on battery strength indications, maybe you need to have that beacon further tested and/or replace it.  Something else may be wrong with it.  If when tested in transmit mode and it's performance drops with battery strength, I'd throw it away. I'm presuming the only way you'd know would be if your partners beacons don't detect your beacon until they are closer to your transmitting beacon with weak rather than stronger batteries (?) 2) All beacons I've used perform acceptably in both transmit and receive mode when battery strength indicates at least down to 10%.  Just today I turned on a Pieps DSP, while conducting a field trip, that had not had its batteries yet changed out this year.  It read 0% battery strength when turned on; it nevertheless transmitted and when switched to search mode quickly began its search routine, picked up the transmitting signal nearby and indicated the transmitting location, allowing a  relatively quick search.  3) I've gone from also changing mine out when they got down in the 70 % range to being comfortable with them into the 20's, when I'll change them with fresh - or before a big multi-day trip.   I arrived at this from watching battery strengths fall in all of the various digital beacons over the last 5-7 yrs with no noticeable performance degradation.  4) I find no comfort in anyone's 80-90% beacon strength in itself.  Instead I'd rather know they just spent several dedicated hours last week or month doing a variety of beacon practice exercises, on snow, with buried beacons buried to at least 3-4 feet, with the beacons laid in at various orientations so as to change the transmitting signal's pattern.  And, that they've taken a companion rescue class or preferably a Level 1 or better.  Good tools in unpracticed hands make for poor results.  5) I think there is great value in fully using up our batteries, as alkalines are not readily recyclable,  have generated a significant amount of energy in their production, contain various toxic metals, and cost us $$.  That being said, taking them out at whatever percentage you feel comfortable with and using those residual batteries to power less critical devices is great.  6) I too carry extra batteries, but if I think I might need to change them out for use in any critical device I keep those extra batteries in an inside pocket  where they can stay warm and be immediately effective at full strength.  Keeping them in your pack is exposing those batteries to the steadily dropping temperatures in your pack - especially if on overnight trips.  Gerry H