Of all the different devices I've owned over the years, the only one that had a battery go bad was the BlackBerry 9000, which had a removable battery. I got it in May 2009, and the battery died in July 2010.
I haven't had battery issues with the Nokia Lumia 900 (from 2012), Nokia Lumia 920 (from 2012) or Moto X (from 2013). The batteries on those devices are sealed, but they all lasted longer than that of the removable BlackBerry 9000 battery.
It's not always about the battery going "bad" its the case of diminished performance. Its like the old adage about how to boil a frog... turn up the heat slowly and he doesn't notice. Same for battery... degradation happens slowly and you get the feeling that your device is getting old... 'maybe its all the apps' so you reset the device, but no. Then the blame starts going to the latest OS update... maybe my 'old' device just can't handle it.
While those situations COULD be a factor... it can be shocking how a brand new battery compares to one that's 1-2 years old - and had been subjected to charging nearly every single day... I've been through the above situations myself for each of the past 3 phones its been a wake up call when I finally get around to buying a new battery or two.
Sure, I could still be using my original Note3 battery... it just doesn't last nearly as long... and like I said... until you see that sudden jump in battery life with a brand new one in there... you MAY not realize how much you've been dealing with fast discharge when you really didn't need to. YMMV, but I've had family members swear up and down its not their battery... until they realize how much of a difference it makes... and this goes for everything from phones, to Wii remotes, to rechargeable AA's. Batteries don't last forever, folks. And as much as we charge our phones, they're probably getting more than 365 recharge cycles on them per year. That's quite a bit.
I still see nothing that convinces me that a sealed battery is better than user replaceable in the Note5. Only benefit being maybe slightly smaller. I've got small hands, but never had a problem with Note 3 size... but I'll give that to you if you felt the previous Notes were just a bit tough to handle.... this could be a tangible real world benefit. (Though the slippery back I think about negates that advantage, IMO.) But at the cost of convenience and flexibility for others who otherwise might have been interested in the device.
I'm sure those that get it will enjoy it. I don't think it will be a lemon of a phone or anything. Just disappointed as a Note fan that it suddenly changed too radically for me to have a strong interest in it. The only reason I keep posting, is it seems people just don't get it why in this day and age people want something that has flexible use cases.... expand-ability... or just does what we've come to expect previous generations to do; or they think we don't know how to use these magical new fangled gadgets... and I assure you... that is not the case. I think its fine if you want to use a device without those features... its fine that my wife and friends use an iphone (and we all get along just fine.) The sticking point for the Note series is it USED to have these... they USED to be advertised features of the device. Having those options didn't dissuade people from buying the device - it was easy enough not to make use of those features... they didn't get in the way of anything.
And if the argument is 'get over it because that's the way everything is going' then that's a sad state of affairs. Because if that IS the way everything is going, my time with Android itself may be limited. If there is only a couple generations left of having options, and with the apparent continual problem of Carriers getting in the way of features/updates/critical security patches and Google's inability to stem that; then the benefits of being an Android user are less and less. (I'm still a bit bitter that my wife's iPhone can do NFC tap to pay... and I've had NFC on my phones for 4 years now and haven't been able to do it.)
I've loved having the choice the Android ecosystem provides... but as that dwindles those other flaws I mentioned become more apparent: TouchWiz becomes harder to swallow, device/carrier removal or not adopting new Android features... and the dreaded "F" word become bigger factors that I may not be willing to accept a few years from now if this trend continues. This move by manufacturers (not just Samsung) could just be another factor pushing more users of the platform away.
I'm not an Apple or Mac guy by any means... its just getting harder to see the difference - and in some cases easier to see some benefits of the other side - as time goes by.