Do Garmins last for a full IM?

Not sure what you're asking, Garmin gives it a "typical "battery life of 10 hours, I wouldn't expect it to last longer than that, certainly not >50% more...

I would think a 15-hour finisher would take longer than 10 hours on the bike and run, even if he didn't turn it on until leaving T1. 

Two Garmins, I can't see why this wouldn't work.

Antagonizing a tapering Ironman has got to be hazardous to one's health...

At my house, my wife often tells me "What's mine is mine and what's yours is also mine."

Not sure if that applies until you get married or not. 

I'd like to add nothing usefull to this thread, as usual.. No the garmin wont last,, I was thinking of doing the same thing, using one for the bike since it's easier to see HR and then use another for the run.  I'm thinking that I'm going without for both. Once I'm on the run part it would be nice to see my pace/HR to make sure I'm going ok. but by then it doesn't matter.

are you going to wear a regular watch/HR monitor for the race ??could you set that up ??  Do you want any HR info for the 2nd garmin. I'm not sure if both of them will pick up one HR strap

Make her happy let her use two

We know you are a kind, sweet, supportive BF as you have shown over and over to Karen. 

It makes the whole thing simpler other than getting the signals to use two and if she need to use the back light it will suck more battery life out.

Karen I found on the run I couldn't hear my beeps for my run/walk intervals because the fans were so loud..seriously.  I suggest having a back up plan if that occurs.

Won't last.  Mine barely made it through my HIM (7:20).  But I had all the functions on AND I had it on before the swim.

As much as I would like to have it, I will just use my Timex to check HR and bike computer...

I think you would be fine with a "cheap" watch that kept time for the bike and use the Garmin for the run. AND you'd still have the cheap watch as a back up for the run.

You're going to rock the race!! <--- Meant for KSH obviously since OP isn't racing.

btw..remember, I lost my watch during the swim and still made it through the day

At LP when I caught up to docswim he commented that he was approaching that 10 hour mark and he was surprised it was still working.  Well, it crapped out about 20 minutes later or so while we walked together.

The idea of 2 sounds pretty cool if you really want to have all that data.  But this is your first, and it will be whatever it is so I personally would just relish in the moment and screw the gadgets.

But that's just me!

I am using my husband's garmin without the HR strap for the bike, and mine with the hr strap for the run.

I've never really looked at my HR during long rides. I just have gone based on perceived exertion. However, I do look at it a lot on my run. Mostly because I find I sandbag a lot when I start to get tired.