If you have inxi 2.3.0 or later, it supports battery condition output:
Battery BAT1: charge: 39.4 Wh 90.9% condition: 43.3/49.0 Wh (88%)
This is very useful to at a glance discover your actual battery capacity (condition:...).
You'd be surprised at how quickly you can lose battery capacity, depending on your use and charging patterns, basically a lithium ion battery loses capacity at every charge, it varies, but you have between 500 and 1000 full charges. Trickle charging I believe drains the actual capacity even more, but you can google questions about how to maximize battery life/capacity over time, that's a different question.
When I first checked all my battery capacity, I was actually shocked to learn how much capacity some of my batteries had lost, some were only at 15% of original, which means, less than 1 hour actual life, for example.
There other ways of getting battery information, inxi for example gets the data directly from /sys, which is where all tools get it as far as I know.
Note that a standard battery icon monitor in your taskbar will NOT show you the capacity state, it will show you the percent charged of the real capacity, for example, if you are at 50% capacity, and your battery monitor shows 98% charged, that means that you have 49% of your original starting capacity of 100% available.
To see what your system is doing when it's just running, run:
to see cpu use.
inxi can also show you top cpu processes like this:
which will show you your top 20 processes sorted by cpu consumption.
ps aux also will show you this but it's harder to read.
In answer to your question, is there any way to get the battery life back, no, there probably is not, it's a physical event that happens either around the cathodes or anodes of the battery, I forget, but basically that breaks down internally and loses its ability to transfer more and more of battery power, which is why all the rechargeable lithion, nickel metal hydride, etc, type batteries steadily lose capacity over their lives, from the first charge on basically. Some people claim you can condition them, which is worth trying since it doesn't cost anything, but I haven't personally found that helps much, but it's worth trying, but if you have 50% capacity, that's what you have.