26TH JULY
The XL_STAR kit arrived last night.
As a bonus, all of the crosshair LEDS are installed and also got a coin battery holder.
Thanks very much element14!
The coin battery holder is not installed so I'll have to install it.
This is a good opportunity to use my 10mm soldering iron tip. My set of iron tips ranges from 0.4mm to 10mm. Here are a few pictures of them.
0.4mm, 1.2mm, 10mm tips.
Almost all hobbyists, professionals and even manufacturers have the soldering iron temperatures set far too hot. Many use temperatures of 350 degrees Celsius.
All this accomplishes is to burn the flux to a cinder, reduces the lives of the soldering tips and exposes components and PCBs to unnecessary temperatures.
Montgomery Scott (Scotty) from Star Trek used to say "How many times do I have to tell you. Use the right tool for the right job!"
The hint is to use the right tip for the right job and a correct technique. This allows a lower temperature to be used.
For this job, it is obvious that the 0.4mm tip is far too small and the 10mm tip is perfect for the job.
I use chisel tips as this provides sufficient surface area for the heat transfer.
A bit of testing show that the solder on the XL_STAR melts at about 240 degrees C so with my soldering set to that temperature the holder was soldered.
Some would argue that the large thermal mass of the lithium cell holder will suck away the heat from the joint and so it does.
The soldering iron must be able to deliver enough power on demand to keep the joint the right temperature and you need to ensure that this power is transferred to the joint.
A mostly forgotten item from an electronics workbench is flux paste (Order Code 1850216 or similar).
This is actually an essential item and can be used to greatly improve the heat transfer.
Flux remover is another forgotten but essential item. There are many brands and types available from element14.
There's even a "No Clean Flux" remover too! 
If you can't get the joint to heat up enough then a little more temperature more can assist. (For Pb free, 280-290 degrees C is acceptable. Avoid exceeding 315 degrees C!, Lower for 60/40 Sn/Pb.
I used my 150W (Yes 150W!) ERSA iCON 1 soldering iron (Order Code 162358) to solder the battery holder.
This iron monitors tip temperature and adjusts the tip temperature as necessary whether it requires more or less.
This picture is from the online catalogue. Don't use the temperature as indicated on this diagram on your XL_STAR unless you want to risk damaging it!!
Here is a demonstration of heating a large area to 200 degrees C. Similar results would have been obtained if the iron temperature had been set much lower because the thermal mass of the large tip radiates the initial spurt of energy with 150W heater recovering the tip temperature very quickly.
Fast forward to 3m02 for the large area heating test.
Here is a photo of the resulting solder joint. Good electrical contact and good mechanical strength has been made without any burnt flux or PCB damage.
