Not sure why every Oasis vs Voyage or other kindle discussion has to always go the same way with the battery issues. I have a K1 from 2008 and a K3 from 2010. I have a basic from 2012? can't recall now, a paperwhite from 2012? Again, can't keep up with the years. I have a Voyage, whenever that came out and bought the Oasis as soon as it came out. All the batteries on all of my devices still work. They were all heavily used with totally random ways of either topping off or going down a bit more. Now the older ones mostly get charged once a month.
So yeah, not worried about any battery with the Oasis. I doubt I will still have the same Oasis 5 years from now. So ask me again in 3-5 years to prove to anyone that the battery is still working on it.
As to the actual question of the OP. If you are happy with your Voyage, you can't go wrong with it. For me, my Oasis is way better than my Voyage. Yet the Voyage is a very nice device, overall nothing wrong with it. But for me, I can hold the Oasis for longer and much easier. The small bezels on the Voyage did cause me to have it fall out of my hands. I cannot use a cover on it as its too heavy when i read. It goes in when I put it down or carry along.
The actual real buttons are so much more pleasing for me to read with than the haptic. No more cramping. Those are very personal things though so it depends if that is important to you.
My screen on level 11-12 is the same on both devices. Same contrast, same brightness, same tone. I can turn the light on the Voyage higher without having any issues all the way to highest. I wouldn't be able to read on it past 13 or so, so its a moot point. My Oasis starts showing a couple of brighter cones on the left as I turn it up. But again, I cannot read in bright light like that. I don't go higher than 12 at the most in daytime and down to 8-9 at night.
So the screen on my Oasis is not quite as good as the Voyage. My Voyage is pretty flawless with no cones or anything. I do not see the cones on my Oasis though about 90% of my reading time. Only when the day turns to dark at some spots in the house do I notice it a little if I stare at it. Which now I just read.
For me the Oasis design is so exiting and ergonomic, it was worth the price. Not since the K1 has a ebook reader been designed so well IMHO.