BMW "maintenance free" battery ????

ran the radio in my E36 only about 45 minutes with the engine off and couldnt start the car, got the clicking sound. got a battery boost a.drove around and car starts fine.
looked at the battery and the water was low on 4 cells so that the top of the plates wasnt covered .
so i added water. are these batteries really maintenance free ? then why does the water disappear ? how do i test to see if i need a new battery ?
car is 8 years old
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When a car battery "dies" it happens very sudden - one day it will start, next day it will be completely dead.
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Exactly. Since you've been on borrowed time for at least 3 years, replace your OEM battery!
Tom K.
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If the car is 8 years old andthe battery is the original, you'll want a new one soon.
Adding water was a good thing, and you should be okay now.

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