Battery replacement Warning Light

Hi there from New Zealand,

I need some advice please, my 2016 Octavia VRS estate recently started showing a warning light " Place in P and proceed to a work shop", something to that effect. I've only owned the vehicle 5 months brought second hand off a dealer that came with manufacturer warranty. The sales rep said could replace under insurance as there was no error code, told me to continuing driving, it was safe to see if it continued. there days latter the battery died after work one night, just managed to get it turned. The dealership said dead battery, jump start, which I  did then eventual it just died in the middle of the rd. My question is wouldn't the cars system give me some warning that the battery was don its way out? My issue is if its  the warning light which turns out to be be a gear input selector sensor had anything to do with the battery failing ? 

My question is wouldn't the car let me know about the battery before it was completely died? 

Thanks in advances

Confused Kiwi