First you will need one or two spare batteries. I purchased mine through Amazon, hassle-free, and have included links to the products on this blog if you wish to do the same.
I only recommend purchasing OEM Samsung batteries for your Galaxy, but there are options out there for off-brand, non-Samsung batteries that have more capacity than the OEM battery does(2600mAh). I have included some examples of extended battery options at the end of this post.
Next, you will need a spare battery charger. This will charge your dead battery while you use the charged battery. Having this is essential to keeping your phone charged throughout the day, 24/7.
And that's it. Now, if you choose to buy two batteries (which brings your battery count up to 3, assuming you still have the original battery), you will have one being used in your phone, and you can carry one in your pocket/purse and leave the other battery charging at home. That's how I did it. The best thing about these batteries is that they're super lightweight and convenient. I rarely even notice it in my pocket.
Remember, the best way to "train" a new battery for maximum charge capacity and longer life, is to charge it completely and then let the battery die completely, and repeat for at least the first five uses. Wait until your phone is under 5% before swapping it out with a fresh one.
I can assure you this is the exact method I used for my Galaxy S4 and I could not be happier with the results. I've had this set up for a couple months now, and I have yet to experience a situation where I am completely out of battery life. And the best part? It all cost less than $40. That's a bargain for the use I am getting out of it. Outsmart your smartphone and experience the full potential of your Galaxy!
Another option is to purchase an extended-life battery. These batteries are larger and come with a special battery cover door. These batteries have a capacity of between 5000 and 7800mAh, as opposed to the OEM's 2600mAh capacity. The only problem with these larger batteries is that most phone cases will not fit. Be sure to read available customer reviews on non-Samsung brand batteries that you may consider purchasing.
Extended Battery + Cover Combo for Samsung Galaxy S4 made by reputable brands like Anker, Hyperion, Stalion, etc
I hope this blog helps with your Samsung Galaxy S4 battery life issues. Power to the Android People.