I keep seeing the term AGM thrown around whenever I read about car batteries and honestly I've been nodding along pretending I know what it means, but I've finally decided to actually find out because I'm about to spend money on one. My 2018 Audi A3 needs a new battery and I've been told it specifically requires an AGM type, not a standard one, and if I get that wrong apparently it can cause all sorts of problems. I found a piece on what an AGM Varta battery is and how it works that explained the basics, something about the acid being absorbed into a glass mat rather than sloshing around as a liquid, but I'd rather hear from people who actually own one about whether it makes a real difference in day to day use. The thing I don't fully understand is why some cars need AGM and others don't, and whether it's just about the start stop system or if there's more to it than that. I've also read that AGM batteries charge differently and that some older chargers can damage them, which makes me nervous about letting just anyone touch it. Is that true, or is it one of those things that gets exaggerated on forums? And does the fact that it's sealed mean it lasts longer, or does that just mean you can't top it up when it starts to fade? I'd also like to know whether the premium you pay for AGM is actually worth it, or whether people just buy them because that's what the manual says without questioning it. If anyone has owned one for a few years and can share how it's held up in this heat, that would be really helpful, because I'd rather understand what I'm buying than just hand over my card and hope for the best.