Don't think the FCC would care, the FAA might not like you not following the ICAs for the ELT, but as an EAB operator probably not a big deal, but I don't play with any EABs at this time so I don't keep up on the regs there.
I have been over this with them.... All they want for me to comply to the language in 91.52 is to use a D cell battery that has a date on it and Duracell is not the only manufacturer to provide that dating option. TSO is not required in an experimental and the warranty for the ELT ran out years ago.
My reasoning for not using Duracell.
1- The first year I did my conditional inspection I removed the battery cover for the ELT and there was evidence that 4 out of 6 of the MN1300 were leaking.... So , I called Ameri-King and told them what I found.. Their comment was " yeah, we have seen that happen lately". Being concerned, as they should be, they sent me 6 more MN1300's..... The problem was they didn't have the same ( best used by ) date on the batteries and according to their manual you CANNOT mix batteries with different dates.... So, I call them back. It just went down hill from there. Ps, they did want me to send the bad Duracells back to them... I sent back the new ones and kept the leaking ones, which I still have here along with pictures of them I took in the 450 just as I removed the cover.
2- I had purchased a high end Laser Transit for my construction business a year or so earlier and by shear coincidence it was needing new batteries too as I was getting ready to start a 7 figure commercial project,,, So, I take the battery cover off that device and low and behold the 4 MN1300 Duracell batteries that came in the Laser from the factory had leaked and basically ruined the 2,300.00 unit...... That would lead me to make my second phone call that week to an entirely different manufacturer with the exact same problem.... Those guys knew about the problem and had me ship the laser back to them with the Duracells still in place...
They got it a few days later and their engineer called to say my unit was trash, that it was Duracells problem and that they would fight it out with them.. They sent me a brand new laser with a different brand of batteries in it... Now that is great customer service.
Google "leaking Duracell batteries" and watch what comes up...
Seems Duracell had switched the manufacturing process and location of the plant and didn't do any QC.. I have heard they lost millions in paying out for damage claims... Since then I have lost all faith in them as a supplier of batteries for anything I own. YMMV.