I fitted a cheapo "Vanfit" battery to my ex Disco 4 years ago, still fine when the ol girl went to new owner. We fit Varta batteries to the trucks that come in to us, pricey but reliable. My Moto Guzzis have Varta batteries, currently 8 years service and still very much ok. Try a local independant motor factor, believe me, the mark up on batteries is , well, a lot.
(100% quite common at dealerships etc)
Regards, Bill