Does my MacBook battery have an issue? It's been nearly 1yr &amp; 6 months since I bought my MacBook 13" 2015 retina. 
Now, the battery only holds 57% of its original capacity. Number of charge cycles is 234. This battery can hold only 2 - 3 hours.

Is this normal? I have no any warranty now.
Try remembering your usage of the battery. Is it always plugged with the AC charger? How many times did you go from 100% to 0? Did you leave it discharged for a long time? This all cuts down you battery life despite having only 200+ cycles.  

You can though try a calibration procedure. Charge you MacBook to 100% and stay plugged for 2-3 hours. Then use it as usual and let it go to 0. Leave it for 5-6 hours discharged (overnight probably) and then charge back to 100%. You will see change in you battery life mAh. If you had never done this before, probably you would like to do this 2 times. It is recommended to do this procedure once in one-two months.

You may track how you battery behaves by entering in terminal the following code:

pmset -g rawlog


It will show current charge, current battery life, design battery life, drain, remaining charging/discharging time etc.