Right, I bought a large when I would normally buy med and it fits great.
The fleece has two pockets on the inside of jacket to hold the battery packs and they are held closed with Velcro.
The battery packs (with batteries) weigh just 105g each and the whole lot weighs 546g.
I fired it up and within 120 seconds my thermometer showed a temp of 44.2 C. Very quick and toaster.
The heating patch appears to be woven wire ins rectangle of each breast plate measuring approx 6x4 inch.
I'll have to see how long the battery lasts and check the temp fluctuations over this time tomorrow.
The inside of the jacket does have a sort of silk lining along the breast but it feels toastie even without the heating unit on.
I'm planning to turn the fleece inside out and use it to pre- heat my sleeping bag.
(Above image is upside down)