Originally Posted by egads
The voltage is not really the issue. What you need is a load test. That is how the health of a battery is tested. If your Insight still has it's original battery, it is beyond time to replace it. Unlike other vehicles that use the underbody battery to start the car, the battery in the Insight is barely used at all. That actually makes it wear out faster because it is not exercised. As a side note, a good battery would show closer to 14 volts.
Agree 100% on the load test and the replacement timing.
Disagree violently with the bold/italics
There is an initial period of "exercising" where lead acid battery capacity improves if it wasn't done at the manufacturer (almost never is). The idea that the battery wears out faster because it's not exercised is completely off the mark.
Beyond the initial forming cycles, every cycle deteriorates the battery. Period. The deeper the cycle, the greater the deterioration. Additionally, when lead acid is at an SoC at anything less than 100%, it is deteriorating from just sitting there. This deterioration accelerates at lower SoC. This is why 12V batteries become ruined after several months of sitting.
Lead acid batteries in Honda IMA cars fail because the cars keep the 12V at lower SoC. Float voltage is typically around 13.6 for most automotive 12V batteries, which is where non-hybrids keep their 12V levels after an initial 14.4-14.7V top-off charging.
I routinely monitor 12V off a cigarette lighter voltmeter. It's rare I see anything in the vicinity of 13.6. There is often an initial voltage of 14.1 after the car is started, but it's typically in the 12.8-12.9 range.