Depending on a number of things (time, effort, cost), replacing a battery can be more problem than replacing a device.
Of course, this is by design.
If we all refused to buy devices that have built in batteries then this wouldn't be a problem.
Anyway, a new device (likely with a replaceable battery) can be had often for the cost of a replacement battery.
This cheap device (~$50 USD) would get you by until you are ready for a replacement of your choice.
Not to mention that your old device could still be used at home for storage, a mini tablet, camera, etc., so long as it is plugged in.
This can be more useful than you may think.
Along with the cheap device I mentioned and a couple SD cards that you probably already have, your device that you use away from home can get a break when you get home, your storage capacity is greatly increased, and the possibilities of your device use increase as well.
I currently use three devices, two identical and one not.
I had a battery issue with one, and it was just as cheap to get another device.
One stays at home, its twin is relegated to Wi-Fi use only (as is its mate) and the unmatched one is my general purpose cellular.
A simple app called NitroShare (F-Droid) allows for easy file sharing among all my devices.
Another option to get you by is to get an inexpensive power bank to plug your current device into when the power drops to the unuseable level.
At Wal-Mart there is a very small portable battery pack that costs less than $5 USD.
This should power your device back up quickly so that you can make it last a few hours more during the day.