I keep chargers always handy and when I am traveling, I have this little gizmo that uses 4xAA batteries (regular or rechargeable). Works great. Tekkeon TekCharge Mobile Power and Battery Charger
Amazon.com: Tekkeon TekCharge Mobile Power and Battery Charger: Cell Phones &…
Besides all of that, I am not surprised how much unreliable battery powered smartphones are becoming. And this is not only Vibrant, I am talking about other models too. Everybody are trying to stuff these phones with power-hungry super screens, sensors, more complex RF circuits to handle higher speed demand. At the same time the marketing people for the same company tells this phone has to be slick and thin as possible because competitors already did it. Engineers probably smile and poke in the heads thinking this is not possible. Still, marketing wins and company agrees for limited solution which in real like brings us all down when battery dies unexpectedly. You can shove these battery ratings and manufacturer running time estimates listed in product spec right down the drain, they're worth nothing. They are crafted by marketing for the use where pretty much phone is doing nothing else but what is listed, meaning you do not have apps running at the background other than the one that is necessary to either make a call.
There is no perpetuum-mobile like battery or another miracle battery cell that wold allow to run this device running like old school cell phone from 10-15 years back. Of course, the batteries are getting smaller with the same power capacity or they keep the size with increased power output. But remember, every new phone with new features demands more and more energy. I know they introduce power efficient solutions and components almost every month, but with all these gizmos built in today's smartphones and all these apps running, there is just not enough juice from small thin battery cell to satisfy typical user demand, nor power hungry smarphone.
I bet if they make new Vibrant as thick as G1 stuffing it with battery pack that would take 3/4 of it's body volume, you would probably get much more talk or browse time on single charge. But now on thin and small cheddar battery pack. Forget it and do not expect more even if you do a replacement. It is physics, nothing else.