Really bad battery

Since I bought the headphones I never had battery more than 3 hours. Now it’s reduced down to max 2 hours. I have had them about 6 months but only used them top 15 times because of the lack of battery time so I use my Bose instead. 10% takes about 6-8 minutes to be used. I charge it in my computer. I’m really dissatisfied because this is not nearly 8 hours what you say it will last. What is the solution?