Charging below freezing point

Firstly you should burry the temperature probe of a digital thermometer somewhere in the middle of the battery pack. Like that it will be less guesswork when the battery is too cold for charging.

Secondly you should think about a heating means for your battery, and some good insulation around the battery to keep whatever warmth there is in there.

Pretty good heating "plates", made to your specification for less than the postage will be, are to be had from here. You should also think about how to power the heating (from on-board or from the grid, or from both, and if you would like a thermostat to automatically keep the battery at a certain temp. (20°C is a pretty good goal), or if you think a timer might be sufficient, after some testing, to get the battery to the required temp. by the time you want to leave or charge.

Not knowing what battery you have (24 or 28 cells) giving a heating wattage is not easy. For 24 cells 100 to 120W heating power should be sufficent.

Best is to heat the prismatic cells from below, as the heat will travel quickly up the electrodes (being copper and alumin(i)um).

Use insulated tools, and make sure you disconnect every row of usually 4 cells from the next. You can start wherever you like, just make sure you never touch both ends of the battery at the same time, and that you do not create any shorts while fiddling with the cell terminals. With a little care you can handle this work without creating any danger for yourself, your cells or possibly your whole Puma.
The cell rows might be fixed to the bottom of the battery box with double-sided adhesive tape, which might be pretty hard to pry loose...

Intersting, Mountain just posted here that there still are 28 cell-Pumas around???

Yes, unlike AC, where the potential is relative to the earth, with DC batteries, a circuit has to be completed through you body between the positive and negative terminals. This is hard to do except deliberately. Even then, nothing usually happens except some slight tingling if your skin is dry. I've touched the the terminals across the pack (80V) with dry fingertips (of the same hand) and noticed nothing. But for peace of mind, just remove the interconnects at a couple places first to make it impossible to be exposed to the full pack voltage.

The voltage of only a few cells can kill - but only under very particular conditions. I recall a story about a guy who killed himself playing with a 9 volt ohmmeter - he apparently wanted to see what the minimum resistance through his body was so he sharpened the probes, an poked them into fingers in his right and left arms so they penetrated into capillary blood vessels - the electric current through the salty low-resistance blood from just 9 volts caused an instant fatal cardiac arrest.

Another thing - I'm not sure what type of BMS your scooter has, but some BMS's can be damaged if they stay are connected to the pack while the pack is worked-on. Hopefully there is a connector at the BMS to disconnect all balancing wires to the cells before working on the pack.