My previous battery lasted for almost 4 years, drove my car almost everyday. Just changed it couple of months ago when it gave me one second silence during cranking the engine in the morning, so it's the sign that you should never deny. On the evening, I changed it straight away.

I saw some sellers are selling some kind of 'battery life indicator' that to be put in the engine day, don't know how accurate it is.

My car is 1.5CC, just an aftermarket HU, and the previous battery serves me well. Even though it's a maintenance free battery, monitor the behaviour. I personally count how many cranks that it takes to start my car everyday.

For my brother, he's using wet battery, the one that requires owner to topup the water on periodical basis. His reason is, "I want to know what is going on in my battery".

So, my conclusion is, it's very subjective to judge about maintenance free battery and regular battery.