FEEDBACK: I WROTE to you a couple of months ago about the baffling problem I had with my Nissan 1400 bakkie with a six-month-old battery that wouldn't last even 20 minutes after leaving the parking lights or radio on.
I can now report the outcome of this riddle: the battery was found to be a dud! After a long quarrel they ended up giving me a brand new battery. Now my faithful seven-year-old buggy is back to its winning and reliable ways. Thank you again for your kind advice. Mandla
MANY THANKS Mandla for letting us know the outcome of the puzzling problem with the bakkie. All credit to you for sticking to your guns until they gave you a new battery.
The fact that the bakkie is back to its old self proves conclusively that the battery was faulty, so the dealer should be ashamed for trying to obstruct your warranty claim.
Your experience shows how important it is to test a suspect battery correctly. Unfortunately, for the average DIY owner this is easier said than done.
There are two questions to ask. The first is how fully charged is the battery. (You need to know this otherwise you might be condemning the battery while the real culprit is a lame alternator that fails to charge it properly).
Any basic multimeter will answer that question: you let the battery rest for 10 minutes after a longish daytime drive, then put probes on the battery terminals and read the open-circuit voltage.
If it shows 12,65V or higher the battery is fully charged. A reading of 12,45V means it is 75percent charged, and this is still acceptable, but anything below that indicates a problem in the charging department.
If the battery is at least 75percent charged we come to the really important question: can the battery produce the heavy current needed by the starter motor long enough to start the engine?
The only way to answer this with certainty is to draw a heavy current (say 100 amp) for 15 seconds while watching how the battery's voltage drops. If it stays above 9,6V your battery is good, otherwise its days are numbered.
On a really bad battery the voltage will drop (below 7V) in a few seconds. This is called a load test and it should preferably be done by a trained technician using professional equipment.
It's a common mistake to do only a state-of-charge test for the battery's current-producing capacity. You can't. Only a load test will provide information about the battery's "staying power".
As it happened in your case, doubts about a battery usually arise when the starter motor becomes sluggish or goes dead. There is a simple test that any car owner can perform to see if the problem is the battery or the starter.
When you get home switch off the engine, then switch on some current-drawing accessories - headlights on high beam, for instance. Let the battery supply the current needed for about 10 minutes.
Then get in and blow the hooter. If the hooter remains strong for half a minute you can be fairly certain your battery is healthy. The gremlin must be lurking in the starter circuit. But if the hooter croaks there's a problem with the battery.
If the state-of-charge test after the battery is recharged comes up fine, take the car to a reputable battery dealer and ask him to do a load test with the proper equipment. Then you will know, and they will know that you know.