Hi Steve
Totally agree - trouble is you need to be near a mains outlet so if you're parked up outdoors it could be less effective than maintaining your Electrics to get it going. When we used to have bad winters we improvised our trucks to use a small paraffin lamp with an extension tube from the ground up to the sump - it did not need a long time to get some heat into the engine - enough to thin the oil, and it's portable, but on cars they put a tray under so it's a tad more difficult. You have to be desperate to use a starter charger since the spikes they cause can fry the delicate electronics. They reckon the electronics can cope with over voltages of up to 32volt but the spikes can go anywhere. Before using one I would prefer to jump from another vehicle but remember to run the slave for a while to get some in then turn off before trying the recipient since the high current draw could blow the surge diode in the alternator of the the slave - It's when the alternator tries to suddenly push the current instead of the battery.