I just received my new version h51 (all levels current regulated). The first thing I noticed as soon as I turned it on was that there is a much more dramatic difference between h1 and h2. I have read of some complaining about there being little to no difference between the two in older versions. It appears that this has been addressed in the newest one. With the older one it was hard to determine which level you were in. Now there is an obvious difference. I use the same eneloop battery in both lights to make sure it wasn't just a battery thing.Second the the new h51 appears to have a low battery indicator similar to the h502. Different in that it flashes about every 10 seconds instead of 80 seconds after you turn the light off. I measured the voltage with my meter and it looks like when the voltage is below 1.03v the indicator is activated. It flashes on its lowest setting until in my case the battery recovered to above 1.03v. I suppose this may not be a new feature but looked and could not find any mention of it. The older h51 I used to test the high settings was not mine. I gave it back so I wasnt able to test this on his.