Hadn't seen this mentioned but perhaps I missed it, more plumbing hardware than electronic, but perhaps useful for others.
Having tried a variety of plates and heat-sink compounds and tie-wraps to hold these little chips in position on small sections of metal pipe (my rads are fed with fused plastic pipe), I came up with the solution of using pipe clips, the cheap plastic variety from DIY stores and hardware merchants.
The first problem hit was with attaching plated sensor the the boiler clamp nut, it was off by 10c and no way could I get a more accurate reading, presumably angle? Finally found a pipe clip which got hacked in half to fit in the tiny gap in the photo... Some hacking with a Dremel, some soldering to a pin connector, some fiddling around with epoxy and voici....

The gap
The tie wrap in the top of the photo is the original plate mounted version which was "off"..

Having scored on that front with more reliable readings I looked at the roving radiator test kit and realised the same solution might apply so epoxied the chip on the end of some telephone line in a 22mm clamp and it works a treat. Cable and chip fit neatly into the screw-hole, flood with epoxy and done. The pipe it fits is 21.5mm so tighter than a duck's rear end...

As said, a tight fit to a twinwall radiator feed pipe, and a complete swine to get back off even with pliers, but no broken wires or oopsies to contend with, and so much faster to fit.
For those looking to measure metal pipe temperatures, possibly an unusual if fiddly solution, but no need of tie-wraps in the latter case...

Not so much a MySensors build as an example of how even the most basic information can inform changes for the better, in this case space heating.

The system here is fairly basic, an array of DS18B20s, some ultrasonic tank probes and a gas reed sensor, temperature is updated every 5 minutes, the gas updates every 0.05m3...
With winters here down to -20, the first priority last year was insulation, and even though a modern house, the gas bills essentially halved over the year, effectively funding not only the insulation, but replacement axial radiator valves and thermostat heads (Heimeier) to replace the typical arrangement of unknown origin, with spare... But now the MySensors impact..
This autumn's attention turned to the central heating unit, a modern combi unit of good manufacture, installed by a 'certified' heating engineer, but aside what little I knew about condensation boilers and the steep learning curve that followed, I was bemused by the return from the radiator loop almost burning my finger within 10 minutes of the system being fired up. This did not make sense for what I understood of a condensing boilers, which compelled a look inside for the first time, the manual and some googling.

The boiler is a 25kW combi with minimum output 7.6kW, the radiators account for ca 13kW at Delta 60 set for 15c drop (previously set ca 20c drop), settings since day one were 65c and the pump was set at max output of 3, last year's -20 resulted in 13.5m3/day gas consumed, not crazy by historical records, but hmmm.
So now comes tinkering with data from MySensors via Domoticz to inform...
Currently the boiler is set at 55c, the pump is on Low (40 v 84w), but the results are surprising - Slower rising temperature when ON, 42 minutes v 25, but gas use dropped from 0.75 to 0.6m3, but here's the kicker from that longer heating time, not only less energy used per cycle, but longer and thereby fewer cycles per day. Current evaluations are between 15 and 20% savings, so thank you to all the MySensors community and contributors.. ;)

Surprised I'm not bald will all the hair pulling and failed attempts to get there but after a year it is finally working...
The task was simple enough, to measure fluid depth in two tanks, one a sewage holding tank, the other a bulk water tank. Just figuring out which method worked with which board was an exercise in frustration, but the JSN-SR04-2.0 turned out the only one of the two I could get to reliably work.

Despite the industrial look, these waterproof light switch enclosures proved ideal, as the batteries in holders fitted beneath the clear plastic. A little hacking out of the switch 'fingers' with a Dremel gives plenty of space in the base area.
Battery holders are held in plastic conduit which are hot glued to the back of the box poking through the front section aperture.

The top case is a 3v3 WhisperNode with onboard RTC and RFM69, and tucked under the spaghetti in the top left back corner is a level converter. The RTC wakens the Node every hour to initiate readings, and despite a few hiccups seems to be reliable. The WhisperNode is allegedly capable of draining the 2 AA cells down to 0.9v, time will tell...

The lower box holds the 5v ProMini, a small latching relay, and the ultrasonic board, the button type ultrasonic (like parking sensor) is mounted on the end of a 3/4" collar to 1/2" galvanised steel tube drilled centrally through the roof of the 1.34m x 1.67m tank area.

Connection between the cases is via Cat5e in 16mm conduit, 2 cores for I2C, 3 cores for relay control and 3.3v power, 2 cores for 5v and ground to the level converter.

Despite worries over echoes in the resulting space, the tank was emptied last night, and the reading is coming in with the occasional glitch at 1620mm depth from the head, which I believe has a cone angle of 45 degrees.
The Node control of a Relay by On/Off pins to Mosfets may seem wasteful, but I had them anyway. The 5ms on/off of this small latching signal relay boots up the ProMini and seems reliable.
Still to incorporate a WDT/Reset on the 5v as it periodically hangs, and a time limiter on the Node to complete the task, but glad it is all all working semi-reliably, even if some of the programming side I still don't understand...
The 5v tests for 2 consecutive identical readings, the 3.3v tests that it fits within acceptable range, and if not calls for a further reading.

Once delivery of a second identical board from China is done, the water tank should be a lot easier. This one is the more important, as ran out of water previously due to corrosion of the level probes in the tank (3 core cable and short bolts) which stopped the borehole pump topping up the tank, and the hidrofor hit it's cut-off electrode. The level monitoring will give early warning to go investigate long before the bulk tank is 'empty'...

Postscript 12/7/18 - Water tank worked flawlessly from first deployment, but led to concerns over dropping battery voltage.. The problem appeared to lie with the Master sinking power through the I2C lines, but a routine to null the SDA/SCL lines prior to sleeping seems to have halted the decay.
One of the unexpected results of the Sewage Tank deployment was detecting a dramatic rise in level during a heavy storm (85mm in 24 hours) initially thought to be ground water intrusion.
Excavation to the incoming pipe connection to the tank found a round pipe in a square hole (not exactly an unexpected building practice here, now packed out and sealed.
Losing 30% of storage capacity would otherwise never have been detected, so it the deployment has already paid for itself handsomely...

@pepson This reminds of that famous quotation "Any ship can be a Minesweeper..."
"Once...."

@neverdie Would this work ?

@sundberg84 Yeah, this brings back memories, particularly of quite a few hangovers.
I used 3 and four wide fireclay pipes for bottle storage, they were used for ducts back in the day before plastics took over, cable went optic fibre. I noticed recently here they are back in stock in stores as....yep...wine storage racks.... but wacko pricing relatively...
The beauty of the fireclay was it's slow temperature and humidity change, and this formed the bulk of the thermal mass in the cellar I made below the floor.
I used a 150mm glazed ceramic drainage pipe dug in under the garden as a loop (rope caulked joints - anybody remember them), from memory down about 1.5m, both avoiding frosts and baking sun, don't think the temperature varied over a degree all year round, the ground acting as a massive heatsink which maintained a constant temperature all year round.
Only when the hatch was opened did the temperature jump, a small fan kicked in when the hatch was closed and ran for 30 minutes, a second contact switched on the lights and shut them off, long before LEDs were so prevalent, old reliable (until you were depending on them) incandescent bulbs.
That was it really.
Biggest problem I found was humidity in the early days, probably the fresh construction...

@tbowmo Hah, you were lucky, I finally upgraded from the monochrome to colour...

@sundberg84 Easy, one is disconnected... :joy: At 90 degrees? :stuck_out_tongue_winking_eye:

Finally the round-tuit UPS got built after the last power cut clobbered the Controller/Gateway system, lesson learned...
Meanwell AD-55A, 7.2Ah Acid gel battery, two usb 5v buck converters, a spare socket for raw volts, and a 15 euro IP66 box from the local shops.. Some drilling and filing to the lid, couple of brackets, spare bolts, banding, soldering and hot glue...
A bit bulky, but disappears in a void under the stairs, two tiny drill holes let the buck converter leds shine threw...
No monitoring as yet, but sailed through a power cut this morning and the Pi didn't skip a beat.. First up is the Pi's RTC then can put the cover back on the Controller...

First of the winter projects done, just the programming to finish and replacement temperature chips to get (broke the legs off both DS18B20s through clumsiness).
With mains/battery backup and RTC, it will record boiler start/stop and run times as well as feed/return temperatures, and as an aside the inevitable power cuts which plague this part of the world.
The MCU plugs into a socketed backplane hot-glued to the back of the box should removal prove necessary, but quite pleased it is sturdy and all fitted into a slim 25mm deep standard (cheap) box.

@NeverDie Was "starting to warm-up" an example of Texan humour, or accidental, given how this thread started off....?

@Boots33 Well, finally I got some positive results, but not quite as expected...
The JSN-SR04T-2.0 nor the DYP-ME007Y I could get to work on all six variations of sketches tried. Still not sure why neither would work using this 3v3 board even with 5v to the ultrasonic board and dropper resistors on the echo. Allegedly the ping from 3.3v should work.

So, bought and finished today trialling a 5v/16MHz Pro-Mini ;
The JSN version 2.0 nor the DYP would not respond to NewPing, simply churning out zeroes.
Other sketches would turn out fixed numbers and zeroes which did not alter irrespective of the transducer/object distance.
The JSN finally got working with a simple PulseIn calculation loop with a 500 delay. First reading was always Zero, all the rest consistent and rock solid.
The DYP unexpectedly responded only to the SoftwareSerial method originally found to work from a Russian site. The readings are spot on from the start.

Now that they work, I need to figure out if there is a workaround for the 3.3v transceiver node....
Phew....

@ben999 Power input and output remains exactly the same. If you take an analogy of radiated power as a tyre tube, the larger the antenna the tyre tube is squeezed on top and bottom extending the range and conversely sensitivity. Add a reflector and directors (as in antenna beam - yagi) the radiation is squeezed top bottom and back forcing the a lobe out away from the reflector.

@sirzlimz There are two ways to use these devices, the method I found reliable was providing Vdd with power, and power via the drop resistor to the DQ pin (data).
I suggest trying the direct power method by pulling the jumper from line 21 and stick it into 25.
If it works fine, then try disconnecting to observe any difference.

Forgot to say - The configuration you have is called Parasitic Mode, some leave Vdd dead ended, some short ground and Vdd together...

@parachutesj Yes, pretty sure it was @NeverDie who trialed a matrix within the last six months which did what you are looking for, you can search for it on the forum...
EDIT - Found the thread, farther back than I thought https://forum.mysensors.org/topic/8936/6-8-buttons-battery-remote-node

@NeverDie I was answering the original post on potential reasons, not addressing specific complaints.

Whatever improvements can be brought to the forum will be undoubtedly be welcomed, but as a beginner on this hobby I have fumbled my way around and gleaned considerable help getting started just searching on the site. I would hazard a guess that many others are floating around without taking part in discussions.... It's not as if folks aren't generally friendly and helpful...

Just home so opened the Node case and glad to confirm despite ageing my recollection was accurate.
This screenshot is common to the PR6/7 using CH2P if it is a undirectional flow.

Looking at the circuit afresh I see no reason why the internal input pullup of IRQ should not work either through a drop resistor or possibly direct, since all it does is sink the signal, which the IRQ will pick up as Change/Falling/Low. From vague memory of the sketch, mine is triggered on LOW.
1 - Unlike Reed switches (my gas reed duration is ca 6 seconds) mosfets are fast, so the pulse duration is so short it will not register on your multimeter hence the perceived uninterrupted 5v. The PR7 spec you posted says 10ms duration...
2 - If envisaging a standalone radio node such as deployed here, you may be better going with a 3.3v PM to begin with rather than mess about with level converters later...
Hope this helps...

In addition to the above, as @Yveaux pointed out the processor can be run almost to battery death, so only the voltage requirements for the sensors may limit your options to running at 8MHz.
My Nodes were bought as a specific variant with onboard booster, so it is technically possible to build a highly efficient booster, but it's unlikely to come from China's mass market.

But this then touches on the point made by @mfalkvidd, rechargeables have very different characteristics to alkalines (Google for info on battery comparisons performed by others). I went through this extensively before starting up, and no regrets on alkalines.

As @Nca78 referred it also depends on load and duration.
My faster processor executes the radio update on a gas reed trigger then goes back to sleep within ms with no external load, 2 years later the Node batteries read 2v.
The tank monitor fires a 3v ultrasonic routine at 8mA every hour and maintains an RTC, but aside hourly routines is in deep sleep the vast majority of the time. 6 months in and Node batteries are at 2.89v, so over a year is guaranteed... However, without it's onboard booster it is likely the ultrasonic would have stopped working.

A further option to where a sensor needs a higher voltage is to switch on a secondary supply specifically for that sensor. I didn't have much joy with that using a booster due to noise, but it worked fine with a battery pack and VR.
Hope this helps...

@nagelc If there is any frustration leading to folks abandoning DIY in favour of commercial offerings I suggest they would have favoured that route to begin with.
For somebody starting out on this DIY hobby the learning curve can be daunting, the technicalities and terminology may be comfortable for those with experience, it is easy to forget that the learner is essentially trying to decode hieroglyphics in the dark by dim candlelight, ie even the most basic explanations can prove challenging to begin with.
The problem for any forum will be the level at which the information is pitched, as it has to accommodate so many levels of expertise...

@nafees-ahmed The 4 pins are duplicated on the board, they provide I2C comms only (eg to access current time) but no Interrupts etc..
The button cell maintains the RTC, if you disconnect Vcc the clock is kept going and it's settings are preserved, so if your board gets a power cut, everything recovers on restoration of power.