https://www.amazon.com/dp/B01LY08DAA/ref=cm_sw_r_cp_awdb_Jh74yb2CGM16E

I've had this battery since Dec 2016 with no complaints.

Here you go.

I'm on Stock 6.0.1, G900A. I went from 1.5-2.5 SOT with the OEM Samsung battery after 13 months of use, but then bought the replacement Anker battery from Amazon for like 8 dollars and now have 3.5-4+ easily. Lasts me all day unless I use maps/location services/etc. along with heavy multitasking.

Sounds you may just need a new battery.

EDIT: I believe it was this one. Pricier than I remember, but definitely worth it if you are on a year or more on your current battery.

https://www.amazon.com/Anker-2800mAh-Battery-Samsung-T-Mobile/dp/B01LY08DAA/ref=sr_1_1?ie=UTF8&qid=1487792878&sr=8-1&keywords=anker+galaxy+s5+battery

EDIT 2: Seems that the battery I bought specifically is unavailable, so the one I linked in the first edit is a newer one by Anker.

The one I bought last year: https://www.amazon.com/gp/product/B00N8ULV7K/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1