I have a fairly newly converted 2010 Alphard. On a recent trip (NC500 since you're asking :)), we plugged into the EHU and headed for bed. Just as I was dropping off, I noticed the CO sensor was giving a reading. We definitely didn't have anything burning so I had no idea where this was coming from.
However, my wife had mentioned that she had heard a hissing noise which was outside my hearing range, and it seemed to be coming from the leisure battery which is mounted under the R&R seat. I switched on the battery monitor and could see that it was reading over 15V which seemed excessively high. A quick google revealed that overcharging a car-type battery can release, among other things, hydrogen, and CO monitors can detect hydrogen. I disconnected the EHU and the CO monitor returned to a happy state.
Now I am home, I plugged in the the mains and watched the reading on the charger itself rise to 15.3V (see picture). I found a manual for the unit online and apparently it shouldn't go above 13.8V. I have tried setting the mode to 'wet' but the unit doesn't seem to do anything then - the fan in the unit shuts down.
So, before I take it back to the convertors to complain, I wondered if anyone on here had any experience with these chargers and could share that with me.
Thanks
Paul