UPDATE: 2008 Prius fob replacement questions
I went out to start my 2008 Prius today, and it was dead. I used the metal key to open the driver door. The car wouldn't turn on. I noticed that the passenger door wasn't closed tightly, and would have been like that since Wed., so it's possible the 12 volt battery is dead (not the hybrid battery). Both fobs are in terrible shape, the button covers are gone. I have meant to replace, but it is one of those things that I forget as soon as I get in the house. I thought I'd try changing the battery in the fob, and then trying it in the car again. I got the battery changed and tried it, but It didn't unlock the door or start the car. I will get a charger set up, tomorrow, when it's warmer, and try charging the car battery, but I have a couple of questions about the fob, and if anyone could offer advice, I'd appreciate it very much.
Since I switched out the battery, will I have to reset the fob for the locks and ignition to recognize it? Or will the fob work without resetting if the battery in the car is charged back up?
Next, I will order new fobs. I was looking and I see fob shells that are identical to my fob. But if I get a shell, does that mean the the electronics inside the fob I've had all these years needs to be transferred to the new shell? Will the new fob have to be reprogrammed? I saw and watched videos on how to set a new fob, but not sure the routine will work on a fob that old. Can I get a new fob that has its own electronics inside and just have my mechanic program it?
I'm proud that I changed the battery, but I wish I would've thought ahead about the car recognizing the fob after a battery change.
That's where I'm at. If anyone can offer any insight, thank you!
I found my portable charger, the long extension cord, got the lid off the fuse/relay box under the hood to access the quick charge feature, and as of right now, the battery is charging. The hardest part was getting the lid off the relay/fuse box and next hardest was finding the charger. I set the charger on the 2 amp charge, but just read that 10 amp is also considered slow charge, so I think I'll change the setting.
Thank you!
= new reply since forum marked as read
But I can have the mechanic check for me.
The shells I saw were on Amazon, just what popped up on a Google search.
Thanks for the clear advice. 
I would have charged the 12 v. when I realized, but it is cold and drizzly, didn't want everything to get wet. I will follow up, I hope tomorrow
yesterday to try to diagnose the problem. I bookmarked the ones I think will help. When I get back to work on the car this morning, I'll check the manual to see if there's anything about the fob in there.
I'll watch the video you shared after I've had more coffee
Thank you!