I've been using the heated Milwaukee jackets for the past 6 years. With the 2 amp hour battery, both zones (pockets and body area) on high, the battery runs a bit over 2-1/2 hours. There are three temperature settings. The jacket takes 3-5 minutes to fully warm up, and gets to 95f.
Milwaukee makes a 4 amp hour battery in the M12 line, but it's close to the size of the M18 battery. My M12 tools, ratchet, bendy light, IR thermometer, are all lower power demanding, so the 4 amp hour battery isn't something I'm interested in. Milwaukee does make a M18 battery converter that has the plug in for the coat as well as a USB port. With the 5 amp hour battery, you'll get better than 5 hours on high using both heating zones.
The heating elements are graphite and aren't replaceable.
In minus 10f weather, running my snow blower, you stay nice and warm.
If you're invested in Milwaukee power tools, it's a good fit. Black&Decker DeWalt recently came out with heated jackets also, but I don't know how extensive their line is.