Honda Grace Hybrid Won't Start: Battery vs Alternator?

Hey there! I experienced similar issues with my 2015 Honda Insight Hybrid last year. The symptoms were identical, slow cranking, dim lights, and intermittent flickering. Initially thought it was just the 12V auxiliary battery aging, but when I took it to the garage, they found it was more complex. The main problem was the DC-DC converter that charges the auxiliary battery from the high-voltage hybrid system. It wasn't supplying proper voltage, which eventually damaged the auxiliary battery too. Had to replace both components. It was quite a serious issue since it affected the entire electrical system and could've left me stranded. The repair wasn't just a simple battery swap, they had to diagnose the charging system, replace the converter, and install a new auxiliary battery. The car's been running perfectly since then, no starting issues or electrical problems. If your Grace is showing these symptoms, I'd recommend getting it checked soon. These hybrid electrical issues tend to get worse if left unattended. Hope this helps!

Hey thanks so much for sharing your experience! This sounds exactly like what I'm dealing with. It's really helpful to know about the DC-DC converter issue, I honestly hadn't even considered that could be the problem. Can you remember roughly how much you ended up paying for the whole repair job? Also, just curious, have you had any other electrical problems since getting it fixed? Really appreciate your help with this!

Hey again! Happy to help update you on this! After my last post, I had everything checked out by my mechanic and turns out I was pretty lucky, it was just the auxiliary battery that was defective in my case, not the DC-DC converter as I initially thought. The repair bill came to 290€ for the new battery and labor, which was a relief since I was worried it might be something more serious! Since getting the new battery installed, my Insight's been running like a dream, no more flickering lights or starting problems at all. Haven't had a single electrical issue pop up in the months since the fix. Looking back, I probably worried a bit too much about the DC-DC converter! It's definitely worth getting your Grace checked out soon though, electrical problems can be tricky and it's better to catch them early. Even if it turns out to be something more complex than what I dealt with, at least you'll know exactly what you're dealing with. Let me know how it goes with your car! Always happy to chat more about hybrid quirks and fixes.

Thanks for the follow-up! I actually just got back from the mechanic today. You wouldn't believe it, my issue turned out to be more complex than yours. The DC-DC converter was indeed failing, along with a worn-out auxiliary battery. The total bill hit me pretty hard at around 800 bucks, but at least everything's sorted now. The mechanic I found was really great, super transparent about the whole process and even showed me the faulty parts. Such a different experience from my last mechanic! They ran a full diagnostic test and explained everything in detail. The car's running beautifully now, no more flickering lights or struggling to start. I'm just glad I didn't wait any longer to get it checked out. Thanks again for pushing me to get it looked at quickly, you were absolutely right about these issues getting worse if left alone. Really appreciate all your help and advice through this whole ordeal!