If you go to a battery agency, rather than a service station, you can often buy a battery cheaper if you ask for a 'factory second'. These batteries have been on display and unsold for more than 3 months, so they reduce the price and give you 1/2 the warranty by default. the battry is unused, and you may only get 18mths out of it, or, a year in a bad one, but it's still cheaper than off the shelf. These batteries are sometimes seriously discharged-which indicates it may not be much good as it may not have been kept charged in storeage. Good to know when you want to sell a car and it needs a battery. Gas stations are the most expensive place to buy batteries, apart from marine establishments IME. NB seconds are not necessarily always available anywhere, partic 1-3 months after the first frosts of the year.