Lots of good reviews on the TS-100. Personally, I don't like any of the design decisions. It's "a stunt" that they put all of the electronics and UI and even LCD display into the handpiece. The main benefit of this is that you can unplug it and take a picture of it with no cord! You have to plug it into a power supply or battery, anyway. They could have put the entire control circuit/UI into a connector adaptor on the other end of the cord. And made a more conventional/swappable handpiece for it.
The clones are here, now. You can get the same type of handpiece that is used by the FX951 (the FM2027/8) and it will no longer cost you over $100.00. You can buy Bakon handpiece. You can buy 8801 style (hakko 936) handpiece that takes T-12 tips. The actual electronics to run it can be small enough to fit in the handle, if you like that design. You can essentially make a TS-100 iron, but one which takes T12 tips, which have a great tip selection.
It is trivial to make any of these clones run on battery. They already run on DC. They (most of them, anyway) just need a separate 5V rail to power the control circuit.
Regarding Bakon, I can also endorse it as a capable station. But FYI, you will need to buy or make a stand for it. The tip isn't held particularly tight, allowing it to spin or fall out when cleaning the tip.* And the PSU is only 19.5V. This gives plenty of power, but the tips are actually designed to use 24V. So it's leaving something on the table. According to t12-clone sellers information, you can even run as much as 27V with some of the controllers, but this is considered to shorten the tip life by burning out the heater, prematurely. I have a 24.5V clone, as well. Other than the warmup time being faster, I don't think the practical performance is any different to the 19.5V Bakon for 99.9% of my soldering. So 19.5V is plenty, IMO.
*That said, I think the Bakon handpiece is lightyears better than the 936 style handpieces that come with most of the other clones. And it's trivial to rewire an FM 2208 handpiece with a new connector to use with any of these clones.