A heated jacket is an insulated jacket with thin heating panels sewn into the lining and a battery in a pocket. Press a button and the panels warm up. The technology is simple. The buying decision comes down to the battery.
Most jackets heat three to five zones, usually chest and back, sometimes pockets and collar. Milwaukee's M12 ToughShell, for example, has three zones in the chest and back with three heat settings on one button. The heat in your back matters most, because that is where a jacket loses you the most warmth. Pocket heat is a nice extra, not a reason to buy.
Run times on the box are for the lowest setting. Ororo's 7.4V, 5200mAh pack is rated at about 10 hours on low, 6 on medium and 3 on high. In real cold you will use high more than you expect, so treat the high figure as the honest one. A second battery is often a better buy than a pricier jacket.
There are two battery camps. Clothing brands like Ororo use small dedicated packs that double as a USB power bank for your phone. Tool brands like Milwaukee run the jacket on the same 12V battery as their drills. If you already own that tool system, you already own spare batteries.
Flying is the question people forget. FAA rules say spare lithium batteries must travel in carry-on bags, never checked ones. Batteries up to 100 watt-hours need no approval, 101 to 160 need the airline's approval with a limit of two spares, and anything above 160 is forbidden. To work out your pack, multiply volts by amp-hours: 7.4V times 5.2Ah is about 38 watt-hours, well under the limit. If the jacket goes in your checked bag, take the battery out and carry it with you. Individual airlines can be stricter, so check yours.
Before buying, check how the jacket is washed. The battery always comes out first, and the care label tells you whether the rest can go in a machine. Also check that the battery charges over USB-C, so you are not carrying one more cable.
The short version: buy for chest and back heat, judge run time by the high setting, get a second battery, and keep every battery in your carry-on when you fly.
