Petzl DUO S review

Now that I used it in real exploration situations for almost a year, I can write this full review. So, here you have it:
1) The design
Let's be straight: most of the caving lights from today look the same: a round metal housing in front, usually from aluminium and a metal or plastic case on the back of the helmet, that is holding the batteries or the rechargeable batteries. There are several brands out there (Scurion, Elspeleo, Phaethon etc.) but all look alike. Petzl approuch to powerful Caving light was different: plastic material, ovoidal reflector and a dedicated and patented system for accu's.

The weight
With it's 370g it weigh less than the competition (470 g for a Scurion). The accu is 168g.

The light beam
The light beam is wide on the horizontal axis, looking the same as the one in the old Ultra Vario model. Somewhere between 160* and 170*. In the vertical axis, unfortunately the light beam is narrower than was on old model. And I mean, I can see and feel the difference clearly, especially after I switched straight  from Ultra Vario to Duo S.
The color temperature of the light is on the cold side of the spectrum. Somewhere around 6500* K like the color temperature of photographic flashes. This is not bad by any means because anyway you get use with any color temperature very fast. I just mention this because is useful for "contre-jour" effects in pictures, because you can obtain a similar effect as one of a flash.

The accumulator
The accu case have the same dimensions as was for Ultra Wide and Ultra Vario, only visual difference is that is completely black, the cap is grey and is encapsulated in a black rubber and have the white Petzl logo painted on it. So you can be sure you buy latest model only by it's design.

The differences are inside these patented boxes: 3600Ah accu's that last longer than the old ones (2200Ah for Ultra Wide, 2600Ah for Ultra Vario). Well, how long it last then ? Depends on how much light you want, of course. But as a average, it can stand 6-7 hours before it switch to reserve mode. This is actually a full "normal" caving trip. I think this is the major improvement of this model over the old ones, the accu got real. Of course you should buy from the beginning a second accu together with this caving light. That's a must for long trip or for a bivouac.
The rated power on maximum is 700lm, and for sure it deliver it. You can cover easily with Petzl Duo S a 100 m deep shaft or a big chamber (imagine something like 50 m long, 50 meters tall and 50 meters height).
The modes are 5 and all are factory presets that you can't change:
Mode 1 is rated at 80lm and is more than enough to walk around camp, crawling in tight passages, walking slowly in technical sections of a cave...
Mode 2 is rated at 180lm and in this mode the light starts to get serious. Good beam surrounds you. You can travel comfortable in horizontal and vertical passages. I use this mode much often than the others. Is kind of "de facto" light of this caving light.
Mode 3 is rated at 330lm and is good for observing larger passages, taking pictures, filming and so on... .
Mode 4 is rated 700lm and it provide the maximum light this lamp can bring in the mighty darkness. You can see the bottom of a 100m  deep shaft, you can see the volume of a huge chamber, well...you can SEE !
Mode 5 is reserved for spot only and is 450 lm. Deep light indeed. Perfect for exploring distance spots at more than 100 meters.
There is also a "boost" mode of 1100 lm that you can use for a short period of time (5 seconds) and only if you still have enough power left in your accu. Is useful when you make a long exposure picture or anytime you need a bigger amount of light in a passage. I am not considering this mode a real thing even if on the box of the product it is marketing with big letters that it has 1100lm max light. It's a marketing gimmick.

It has also  a system called "face 2 face" that I didn't tested. This should provide instant dimming of light when you look at somebody wearing a "face 2 face" compatible light. It's a sensor that detects this. More details are here.

Waterproofing is provided by it's IP67 rating which is tested for sinking it at -1m for 30 minutes. I didn't had any problem with it until now regarding waterproofing. Also, the accu's I think are very good sealed because I am still using the boxes from the first model that I got back in 2011.
The reflector is smaller compared with previous models and for sure smaller than the competition. Which is good for tight passages especially. The plastic used seems alright to stand the test of caving for several years. The Petzl warranty is 3 years for the reflector and 1 year for the accu's.
Final thoughts
This lamp is definitly  an improvment over the old model from Petzl (Ultra Vario). The light beam is narrower on vertical axis while having about 160* on the horizontal axis. The volumes you can cover with it are big. Halls, deep shafts, no problem seeing them. It is also smaller which can be only a good thing. The accu mounting system is the best you can get. Clipping and unclipping an accu never been so easy and the system stood the test of time. The price is good compared with the competition (370 euros).
The thing what I'll improve and I am disappointed it doesn't have, is a larger angle of light on vertical axis.
Using 1 accu each day, you'll need to count how many days you'll spend underground and get the accu's accordingly.

The big one, Accu 4, is not made anymore. They were bulkier and heavy. Were not meant to be wear on helmet but I got one for curiosity. Inside of  it you'll find 4 Li-Ion cells instead of 2 but is way better to get 2 distinct smaller accu's than that monster.