There are couple of old books on Hinduism that you can read
free on Google Play. You need to log into the Google Play store and select the
category books.
You can read Bhagavad Gita and several books associated with
Swaminarayan free. All the books written by Sir Monier Williams on Hinduism can
be read free.
When you keep searching you will come across many other
books that can be read free.