During initial purchase 3 years ago I had read about the issues a few had with MAN engines and the engine display reading hours that made no sense. Since then I have never had an issue and assumed the lithium batteries in my engine black box had been replaced. Perhaps they had been but a recent health issue has cost me a very expensive lesson. I have searched past topics on this and what CapJ is saying is spot on. I have now spoken to my MAN dealer and have better understanding of actual issue. Sometimes it is hard to really learn about something until the matter is real. Hypothetical learning is tough in some instances I guess. Here is what happened to me and what I learned. Perhaps it can help others in the future. The Black Box on Common Rail MAN engines have multiple boards inside and one of them has a lithium battery that while the engines are shut off it stores information regarding engines alarm history and hours for the remote display. If power to the black box is turned off for a period of time the battery can run dead and that will cause you to have an erroneous reading on your remote engine display at the helm from that point forward. If you don't fix the issue then when you have an alarm there will be no record stored of it happening for dealer to see from laptop. The actual hours of the engine will be accurate in the black box and a dealer can easily see this by hooking up their laptop and running diagnostic. My dealer said that MAN has not communicated what is causing the system over time to draw down the battery when everything is turned off. Voltage to the black box keeps battery charged. At present time the only MAN authorized fix is to send the one board with the battery to Germany and they fix is for $9700. Are you F*ng kidding me. There is also a unauthorized repair that can be done aftermarket for $4500. What a joke. My dealer is talking to MAN about a resolution that would be authorized and only cost $800. time will tell. Here is how I got myself into this situation. I returned from a 575nm fishing trip that was absolutely epic and the boat performed perfectly. I had a few small engine room maintenance items I wanted to proactively do so figured why not jump on it now and not wait until winter. Just little things to keep MAN's dialed. During this small project I turned the T handles in the ER to off so no power was going to engines while I was in the middle of stuff. I thought that was the smart thing to do. Unexpectedly a few days later I go and have a heart attack. 100 % blocked artery at 40 yrs old. Super active and was playing full court hoops just hours prior. 5 stents later I was recovering. This was completely a hereditary thing. I go by the boat but per Cardiologists orders I am taking it easy. After a few weeks I take the time to finish my maintenance in the ER and button things up. I feel better and boat is back dialed so all good. I leave the boat feeling I am getting back on top of things and later that night my wife goes into labor and by lunch the following day delivers our baby boy. So 2 more weeks go by and while I stop by the boat several times I am not able to really get out and use it. Just check stuff and literally do a walk thru. After a total of 5 weeks I tell the wife I gotta go down to the boat and run all the systems. I never go this long without spending a day on the boat and running systems. I get down to boat and turn on breaker to engine ignition in the salon and remember that I had not turned the main engine T handles back on in ER. After doing so I go fire them both up and immediately see that Port motor engine hours now registers 314039 hours. WTF. I quickly remember my readings 3 years ago on this very site and my gut sinks as I realize having the power off for more than a few days has caused this. I warm them up and make sure all is well, which it is, other than this stupid lithium battery design from MAN. If MAN has a design that requires constant voltage to the system they should inform owners of that or at least acknowledge it. I am diligent about keeping the boat and engines dialed and am completely OCD when it comes to the Cabo. This issues chaps me more and more as the days go by. My dealer said this was a continued topic among dealers at FLIBS and I am not the only owner currently dealing with his issue. We will see what resolution they come up with but I am not forking over 10k for a F*ing battery the size of a penny.