If you own more than a two performance cars, then having a portable battery pack is a quick and easy resource when a battery goes flat. We looked into several portable battery packs that offer additional features like a small 12-volt air compressor, a 12-volt cigarette lighter output terminal, and even a USB charging port for your iPod or portable telephone. Lost in all the hype around these packs is the pack's power source. We looked into them only to discover that all but the most expensive units use very small batteries with generally inadequate cold cranking amps and minimal reserve power. Our personal experience with these units is that if your car's battery is completely flat (which is why you need the jump in the first place), these little batteries usually don't have the power to adequately crank a strong compression-enhanced engine. Sure, you can find a jump box with enough beans to do the job, but they are generally priced in the $400-plus range. We decided to build our own for a lot less cash.
The key to a successful jump pack, if you haven't already guessed, is the power source. The plan is to use a battery with adequate cold cranking amps (CCA) combined with low internal resistance. This low resistance allows the battery to easily push the amps through the dead car's starting system and crank the starter motor. We did some research and Optima batteries offer some of the lowest internal resistance of any battery on the market. Our next step was to find a smaller and lighter battery that would be more portable than a 40-pound Red Top. We settled on an Optima yellow-top model D-51 that is narrower but most importantly weighs only 26 pounds. The key here is that while the battery is lighter and offers less reserve power, it has more than enough CCA to crank over even high-compression engines. We even did a test of this battery back in the Aug. '09 issue (“We Test It”) where we subjected a 10:1 compression small-block Chevy to 10, five-second cranking sessions over a period of one hour so we wouldn't overheat the starter motor. The smaller D-51 battery was still cranking at roughly the same starter speed at the end of the session as a fullsize Optima Yellow Top battery. This battery isn't cheap at $175.97 from Summit, but since we built the rest of our jump pack, we opted for a really good power source. The next step was to build a simple battery box to house the battery along with a 12-volt cigarette lighter outlet we could use for a portable electric tire pump or perhaps a 12-volt light source.
There are wet-cell batteries you could use instead of the Optima, but we really like the yellow battery because it won't leak or vent acid and corrode our cool little homemade box. We've already put our jump pack to use when we forgot to close the passenger-side door on our Chevelle and the interior light drained the battery overnight. After building this jump pack, we realized it makes a great power source for our trips to the dragstrip and road course track days. There's always somebody who needs a quick jump.
Parts List
Description PN Source Price Optima D-51 battery 9071-167 Summit Racing $175.97 Optima 4-amp charger 150-40008 Summit Racing 109.97 Red battery clamp 142501 Del City 3.35 Black battery clamp 142505 Del City 3.35 2/0 Ga. Battery cable 5200255 Del City 89.82 (25-foot) Misc. metal NA Industrial Metal 40.00 12-volt power outlet NA eBay 6.95 Battery cable terminals EFXCBT048 Scosche 15.95 (ea.)
This is our home-built jump pack in service with the Optima D-51 Yellow Top battery. We made the booster cables long enough to set the pack on the floor (rather than on the fender of a $15,000 paint job) to still reach the battery terminals on the car.
Car Craft family member Tim Moore suggested pop-riveting our battery pack box together using angle aluminum, which eliminates the need for TIG welding. We added box length to allow room to store the cables. The black handle is plastic.
We purchased large diameter 2/0 battery cable and clamps from Del City. Cheap start boxes use thin cables that get hot and reduce amperage flow. The Del City battery cable is heavy because its quality multi-strand copper wire. The Scosche battery terminals were left over from an old stereo installation. We used them because they have a plastic cover that will prevent direct shorts should we drop a wrench across both terminals.
We also mounted a cheap, 12-volt power source outlet that can be used for an electric air compressor to add air to a tire. Those little budget pumps will work, but often the power wires are too short to place the compressor close enough to the tire. With a portable battery pack, that is no problem. Plus, you can buy adapters that will turn this outlet into a USB charging port for your portable phone.
We also needed some way to recharge our jump pack and found this equally portable Optima 4-amp battery trickle charger that is perfect for maintaining the charge. Keep in mind that Optima Yellow Top batteries are only fully charged when the static voltage is at 13.18 volts. At 12.5 volts, it’s barely more than 50 percent charged.
