Largely depends on your climate and the type of driving you do. We have a small fleet of vehicles at work, and the oldest is a 2004 RAV4 with ~90k that's still on the original battery. It's been through 7 harsh winters yet starts fine every time. Will probably get it replaced this year, but it just goes to show how long they can last when it's all highway driving.
'15 i3 REX // Capparis // ZGW // ZTD // HK // 20"
20% Tint, Coding, LED High Beams/Signals, Painted Reflectors, MAX2 Hardwire
Past: F30 335i, E90 328xi