Cold weather brings to dealerships and auto parts stores a parade of customers bearing batteries. Customers assume a quick test will determine whether their batteries are "good" or "bad."
The truth is that there is no simple, quick test for batteries. Tests conducted by a major farm equipment manufacturer showed half of batteries warrantied as "bad" were actually "good, " but merely undercharged, low on fluid or had been tested incorrectly.
I'm not a battery expert but have learned a few facts that help me do a better job when testing batteries.
-Batteries should be fully charged before testing. Make sure all cells are filled to the proper level. (Never add acid to a battery. Add only water, and distilled water if possible.) Use a "smart charger" that slow-charges batteries, monitors their condition and automatically ends charging when the battery is at capacity.
-Use a quality battery tester. The shiny chromed battery chargers with slots on the sides that look like cheese graters are "okay" for testing small car batteries but inadequate for testing tractor and farm machinery batteries. The best way to test high-capacity batteries is with a carbon pile load tester. Such testers can be adjusted to put a simulated load on batteries, and do an excellent job of identifying batteries that test "good" but fall on their face when an actual load is applied. FYI, carbon pile battery testers capable of testing farm batteries range from $500 to $700.
(There is a new breed of digital battery testers on the market priced from $50 to $200 that claim to be able to load-test large batteries. I'm uncertain if these lightweight and convenient testers can compare to good ol' carbon pile testers. I've got a mid-range digital battery tester, but haven't yet passed judgement on how trustworthy it is. When in doubt, I still drag out a carbon pile tester.)
-Even if a battery tests "good", check it with a hydrometer. Battery hydrometers check the specific gravity of battery fluid. A certain percentage of batteries test good, but fail under load because the battery fluid is off-kilter.
Like I said, I'm not a battery expert. But I've learned that REALLY testing a battery takes time. Time to allow it to fully charge, time to use a quality tester to load-test it, and time to double-check the battery's condition with a hydrometer. If you haul a "dead" battery to your local battery retailer, slam it on the counter and ask for a "quick test," there's a 50-50 chance you'll walk out with a brand new battery, whether you need it or not.
Not because they're trying to shaft you, but because you asked for a quick test, and the quick test said your battery needed replacement. Sometimes you get what you ask for.