One of the best purchases I've made in recent years was to buy a battery booster pack for my home garage. Folks call them by different names---jumper packs, battery boosters, booster packs--but the concept is the same: they're a specially designed rechargeable battery in a case with an easy-carry handle and built-in jumper cables. Hidden in the easy-carry case are microprocessors and other electronic circuitry that makes the rechargeable battery work perfectly to jump-start cars, trucks and tractors with dead batteries.
The great thing about booster packs is that they're "smart" enough that you can leave them plugged into a wall outlet all winter so they're always fully charged. Disconnect the plug from the wall outlet and you're ready to jump-start any vehicle. Instead of having to drag an extension cord to power a 115-volt battery charger, or find another vehicle so you can use jumper cables to jump-start the dead batteries, you just carry the booster pack to the dead horse, hook up the two battery cables that are built into the booster pack, and you're ready to "jump" the dead battery.
My little booster pack weighs about 10 pounds and easily starts a car or pickup truck. As long as you don't crank on it for a long time, it will start two, three, maybe four vehicles before it needs to be recharged. It cost around $55. At the dealership we use a heavy-duty booster pack designed for starting big diesel engines. It's heavier, around 40 pounds, but its carrying handle makes it easy to lug up and down steps and ladders on combines and tractors. If it's -20 degrees and a tractor's batteries are stone-dead, it might not get the job done, but if a tractor's batteries have ANY power left, that heavy duty booster pack will generally provide the extra "oomph" to start even the biggest 4WD tractors on sub-zero days.
When you shop for a battery booster--and you should if you don't already have one--look for long cables with insulation that will stay flexible in cold weather, cable clamps that are easy to operate with gloved hands, and then match the amp-capacity to the biggest batteries you anticipate jump-starting with the unit. Like I said, the little unit that I keep in my garage was around $55, while the heavy duty unit at the dealership was more in the $200 range.
After spending a lot of years dragging electrical extension cords to the back corners of machine sheds so I could use a 115-volt battery charger, or having to figure out how to get a pickup or another tractor close enough so my jumper cables would reach--a battery booster is worth every penny on those cold mornings when you really don't need any extra frustration.