JeremyW wrote:DarkStar wrote:I'm seeing about 12.3 volts at rest, which is considered only about 70% charged.
That's concerning if true. Lead acid batteries develop sulfation (lead sulfate crystals on the plates impeding current flow) if they sit too long at a partially discharged state. Lead acids love to sit at 100% all the time. This makes them perfect for the float application and partially why Nissan went with it instead of something newer for the house battery. You can give it a float charge and it will be happy for years.
However, I do ask what kind of multimeter you are using to read the voltage. Some of the no-name brands are notoriously inaccurate. I'd check with another meter just to be sure. You should be seeing something around 13.5 to 14.1 during float/charging. My guess is the meter is off by a few hundred millivolts, and the DC/DC is fine.
I purposely didn't check the voltage during float/charging because I wasn't sure if the battery was holding up very well. I just picked up a second multimeter last weekend to perform this test and I'm within a tenth of a volt.
I have a small power backup system for emergencies and I float it at about 13.85 volts (70 degrees F). If I take that battery off and let it rest for an hour or so, it will read 12.8 volts (12.7 volts is considered 100% charged).
I'll have to double-check, but I'm pretty sure I was seeing a voltage of about 14.4 at the battery when the vehicle is powered on. That would be just about right for bulk-charging, but would cause issues once the battery was fully charged (if the voltage doesn't taper).