Corner Wrench: DIY Battery testing; what might you be missing?

If you’re like some shade-tree mechanics, winter’s approach may see you inundated with family and friend requests to check a few things on their vehicles to minimize cold weather surprises. ’Tis the season to pull out the electrical multi-meters and battery chargers. But plain electrical multi-meters don’t tell the whole story about a battery and charging system, and they’re incapable of applying an electrical load to the battery to simulate how it will perform when the engine is started.

Being stranded with a dead battery is likely one of the motorist’s most easily-preventable situations. While vehicle technology has rocketed forward, batteries use pretty much the same design and materials as they did 100 years ago. Yes, their reliability and lifespan have improved, but if they’ve survived three Canadian winters, they at least deserve a 30-second test which can predict their demise with pinpoint accuracy. And seeing that more batteries fail in the heat of summer than in the dead cold of winter, running these tests in late spring would probably save more road-side headaches than doing them in the fall.

Battery load-testers can be purchased for as little as $50, and if you’ve got more than a few battery-equipped engines of your own as well as those of friends and extended family, you might want to invest in one. When preparing to load-test a battery, keep in mind that having a booster pack on hand is a smart idea, because it’s very easy to load test a weakened battery into a discharged state that won’t restart the engine. Batteries need to be fully charged before load-testing them.

But batteries are only one part of the mix, with the other major component being the belt-driven alternator (or generator if the vehicle is old enough). Trying to diagnose a possible alternator weakness with just a plain voltage tester is tough and likely to bring inaccurate results. These situations are made easier with a system tester with an inductive clamp that, when placed on the positive battery cable, will provide an accurate reading of amp flow. These tools start at about $80, but can have an unlimited number of uses when working on almost any automotive electrical issue.

Before removing any cable from an automotive battery, check first for any security systems that might be set off when the power is removed such as radio anti-theft software. Those handy pocket-sized lithium booster packs can come in handy to keep the power supply to the vehicle’s harness uninterrupted when swapping out a battery. They’ve come down in price since their introduction, but are still hard to find for under $100.