Two dead key fobs walk into a bar at the same time? 2013 Prius v Five wagon

This forum has been a great resource, so thanks ahead of time & hopefully someone can help guide me to the correct solution.

2013 Prius v Wagon - 135k miles. Purchased used in 2015 at 24k miles & came with 2 key fobs that both worked. No problems & routine maintenance, oil changes, filter replacement, fluids replaced as rec'd on here.

Problem: Key fob will not lock/ unlock the car. This started after a long drive & the car was parked from Friday evening to Sunday morning. When I went to unlock the doors with the key fob... nothing. No lights or anything left on as far as I can remember.

More details:
1) I have to manually unlock doors with the key & start car by placing key fob against Power button and then the car starts.
2) Smart Key System warning light (yellow warning light of a key with an exclamation point in the middle) is illuminated after starting. I drove 5 hours on Sunday on the highway, and after ~2.5 hrs, the SKS warning light went away. After filling up on gas (kept car on), the SKS warning light lit again.

Troubleshoot:
1) Tried to replace key fob with new battery & tried to spare key, but both do not unlock or start the car.
2) Tested voltage across 12v battery & got 12.85V, but this was maybe 30-45 min after parking and turning off car.
3) Took car to Toyota dealer, they checked the smart key receiver, the fuses, and the 12v battery and all checked out ok. Their diagnosis was that 2 key fobs stopped working and I needed to order new ones ($219/ea) and have them program ($124 for both).

Question: Any other ideas? Should I go ahead and replace the 12v battery to see if this will resolve the issues since it's been 3 years and some on here will replace on that time frame (some will wait much much longer), or just bite the $350/ $500 bullet and see if that will fix it. They dealer says that this has happened one time before on a 4runner...

Thanks all!!

 

Thanks all for the suggestions.

I never had a good feeling about the dealer/ service dept I took it to, but it was the closest one to work (and they charged me $125 just to take a look at it). I have doubts that they really tried to do anything other than swap out the key fob battery, hook it up to the computer and run a few diagnostics tests, and check the 12v battery.

I checked with a Toyota mechanic on JustAnswer, and here was his answer when I told him that the dealer's suggested solution was to buy new key fobs and that they could not be reprogrammed. "Part of that statement is not true. Smart key remotes can be reprogrammed to the original engine ECU and transponder ECU but they cannot be reprogrammed to another car once they have been programmed initially. I have personally reprogrammed many smart keys to the original car that the key came with. In one case somehow the codes got erased and the keys wouldn't work. Have no idea why but when I reprogrammed the program went through and they started to work normally. Let me know what you finally have done to resolve this."

I totally agree that two simultaneous failures of the key fobs is unlikely and with the erratic behavior of the SKS warning light coming on and off randomly with the key in the same location (my pocket).

Next steps:
1) Turn off/ on the SKS system and see if toggling that will work (thanks, bisco).
2) Buy a battery and swap it out (not much more than it would take to get a 2nd opinion & i'd have spare battery when the time comes if it's doesn't solve the issue (thanks, mikefocke).
3) Get a second opinion at my regular dealer, and make sure they try to reset the ECU, and then try to reprogram the key fobs (thanks, ETC(SS)).
4) Buy a new key fob... (no thanks, Toyota dealer)!

 

Well, after driving around like this for 6 weeks, here's a quick update...

1) Turning off SKS system didn't really do much -> the problem remains.
2) Swapped out the 12v battery for an Optoma yellow top -> the problem remains
3) Took it to another dealership, who actually took a more comprehensive look, they tried to reset/ reseed the ECU and then reprogram my original key fob. Doing this led them to discover that the problem in the certification ECU. To replace would involve buying another ECU ($858) with four hours of labor ($125 x 4 = $500), so I'm looking at close to $1400 bill, which is in line with other quotes from the forum to replace the ECU.
4) New key fobs won't work, and I'm glad I didn't give the original dealer that looked at it any more money.

So now I'm unsure what to do. The car drives great still at 140k miles, but $1400 is logically better spent on saving for the next car. It is a major pain to go from SKS smart key fobs to having to pull out the key to unlock it every single time. The dealer rep suggested that an after market alarm would take care of that, but then I'm carrying around another key fob and I still have to place the Toyota key fob near the start button to go...

Any other ideas? I've read that some will try to flash it with 50% success, or just going with an salvaged ECU and then replacing it myself and getting the keys reprogrammed, but I'm unsure if I'm up to the task of disassembling that much...

Thanks for reading!