Sense 2 - Battery life

[Trussman86]

My sense 2 won’t hold a full day charge, I challenge it to 100%, and within minutes I’ve lost 15%. My half the day it shuts off randomly without me doing anything, simply sitting down. My watch is always on button face activate only and screen is always on dim. I thought maybe the last update caused it, but this randomly happened last week. Now I’m thinking simply age, I’ve had my watch for 1.5 yrs, always let it die before fully charging it. I doubt I can get it replaced due to the fact there’s only 1 year of warranty on it, as it was a brand new product when I bought it. 
what can I do, I truly enjoy my Fitbit watch and don’t want to spend a huge amount of money on a new one 

Moderator edit - updated subject for clarity

[LZeeW]

@Trussman86   I hate to be the bearer of bad news, but you inadvertently contributed to your battery's demise by having it discharge completely before recharging.  This is known as a deep discharge in battery world.  This is bad for lithium-ion batteries.  Is it Bad to Fully Discharge a Lithium-ion Battery? 

I'm sorry, but there is nothing you can do about your current Sense 2.