Connecting a Li-Ion Battery to PCB - Is it safe to solder?

I'm working on a small form-factor wearable device that uses a 120mAh single-cell Li-Ion battery for power.
As the form factor is so small, I'd like to connect the battery directly to pads on the PCB without the use of a connector.
The battery is supplied with an integrated PCB for temperature protection. The battery cell tabs are connected to the integrated PCB. There are two wires from that PCB for external connections to the battery.
My local assembly house have said that they do not have the facility to spot weld or ultrasonic weld the wires from the battery to my PCB.
My question is whether or not it is safe to solder the wires from the integrated PCB on the battery to my PCB.
I've seen a variety of opinions on this. There seems to be two basic schools of thought:
1) Simply do not do it under any circumstances.
2) If you do it, keep the soldering iron temperature to a minumum and be ligthning quick when you solder the connections.
Different Li-Ion battery datasheets seem to come down on different sides of this argument. Given the overall low quality of Li-Ion battery datasheets (compared to ICs or connectors, for example), I'm hesitant to accept either suggestion at face value.
I'd appreciate any input on this. Is it safe to do this? For the person soldering the wires and indeed the battery itself? If so, how best to go about this?
Many thanks,