I have had two BMW-brand, made in Germany by Exide, AGM batteries fail without any warning about 3 years ago. Both times the bikes could not be started, even by jumping, and had to be towed to the dealer. (The battery on my F650GS was only 6 months old.) I had the same thing happen with the AGM battery on my 2004 Kawasaki 250 Ninja. Considering that modern FI motorcycles will not even start if they don't have enough voltage, 12V IC motorcycle batteries really worry me. I never had a sudden-death problem with a flooded battery in 45 years of riding, but the latest AGM batteries occasionally seem to suffer an internal short, perhaps due to vibration, and can really leave you stranded.