LITHIUM BATTERIES, being so very dense in energy, can fool you into being careless. They are so compact and quiet, it helps to compare them to a motorcycle 500cc engine turning noisily at 5000 RPM. That's how much danger you're dealing with. Or consider them a welder, ready to weld big steel. If you grip a metal box wrench, tightening a terminal, and swing it across the other terminal, in a microsecond, it will be white hot and give you a crippling burn.
Yet once one terminal is totally isolated and insulated, a battery is meek as a kitten; so your initial challenge is to completely isolate one terminal. First, when you receive your battery, tape up both terminals generously with tape. Then crimp a lug on your large negative lead, and connect it securely to the negative battery terminal. Then glue an insulating cap over that terminal. I use a rubber crutch-tip with duco cement, cutting a notch for the lead to emerge. The other end of that negative lead I attach to a DC circuit breaker (not an AC house breaker) and tape generously over everything conceivably exposed at that breaker. With that circuit breaker clicked off, you are home free! A short circuit is impossible. Glance at it, periodically, to assure yourself. Then, as you wire your system, use electrical tape generously, totally insulating every connection as you go.
Do your battery work in short sessions, so you can keep your mindfullness up. The minute you detect that you're tempted to cut corners, call it a day! Finally, remember to keep a fully charged fire-extinguisher near by, wear safety goggles, and possibly heavy gloves.
