I am writing an android app and I retrieve a balance for the user from a webservice and the user is able to log in and out of my app.

When the app starts I check the shared preferences to see if the user is logged in or out. On correct log in I update the shared pref boolean to true and set it to false when the user logs out.

I need to know the balance in several fragments and I need to remember it when I am navigating thru the fragments in my app. When I return to the "My Account" fragment balance value is lost and I have to call my web service again to check it. 

It the best way to use a string shared pref and update it any time the app starts or when there is a change in the balance. Or am I better to use a static variable in my main activity that can be referenced when the user navigates to the My Account fragment.

Is it possible to overuse shared preferences?