11.8V is obviously not good, but you can't use voltage to decide how healthy a battery is.
A good battery can be down to 11.8V because something in the car is drawing power. Charge it back up (and fix the issue) and it'll be fine.
A completely wasted battery can show 13.8V if it's fresh off the charger, but it won't be able to power anything for very long let alone crank an engine.
Also, a battery should last way longer than three years for most people. I tend to kill them fairly quickly because I have a parking heater that wears the battery down every morning and a 10 minute drive to work which means it doesn't always have time to charge properly. The OE battery in my last car (owned since new) lasted four years. The OEM battery in my Opel (same manufacturer, Varta) was still able to crank the engine just fine but the heater kept turning off in the morning with a "low voltage" trouble code.