The backup generator failed to start three times in the past year. In each case, the batteries were low. Pete was assigned to fix the problem.
Pete took “As Found” voltage measurements and noted the 12V batteries were at only 10.6V. He ran the generator, and measured the charging regulator output; no problem. He connected a portable charger system set to “low charge” (trickle) for 12 hours. Right after charging, he found the batteries were at 12.4V. The next morning, they were down to 10.6V.
He says some load is draining the battery. Is he right?
Pete is on the wrong path, here. In these systems (and in automotive systems), the problem is almost always inside the battery. A rogue load that drains the battery is rare.
Pete could prove the batteries are bad by disconnecting them for a few hours after charging, then checking the voltage. If it’s low, a rogue load didn’t do that.
If he really wants to verify the health (or lack thereof) of the batteries, he will need to get his hands on an internal resistance test set. But given what he has found thus far, it is almost certain that replacing the batteries will solve the problem.
