- Joined
- Mar 28, 2026
- Messages
- 11
Yet another ask-strangers-on-the-internet post; and my second thread on BITOG!
A few months ago, I replaced the one-and-a-half-year-old factory Honda EFB (made by Clarios) with an Odyssey H5 AGM on my '24 Civic. Why would I replace such a newish battery? I thought I saw battery acid leaking. Plus, I wanted parking mode on my dash-cam to last as long as possible.
Everything was fine until I started to experience difficulty starting my car. And, based on the volt readings from my OBD2 gauge, my battery dropped to 10.8 volts when off. Rather worryingly, voltage would fluctuate in the 14-volt range. I've already warrantied the battery, and the replacement is behaving as expected.
The Civic is driven almost every day on a 40+ mile commute (weekends are mostly short errands). While I know Honda's alternator adjusts output voltage based on load, this page by Varta (owned by Clarios) says swapping an EFB for an AGM is perfectly fine. Based on my OBD2 gauge (it may not be the most accurate, but it's what I have), with my foot on the gas pedal under light loads, voltage is 12.4 volts. When the car senses higher loads, the voltage is 14.4-14.6. It only sees that voltage when the climate control is on high, when the lights are on, or when I'm coasting. I know European cars require a battery registration when swapping to avoid overcharging, but I haven't been able to find anything similar for the Civic. The only thing I could find was resetting the voltage monitor through HDS or a similar diagnostic tool.
The electronic accessories installed in my car that may be correlated:
Unless I'm dumb, and my OBD2 gauge always plugged into the port may be contributing to parasitic drain.
Any thoughts before I go ahead and dismiss this as a bad battery? When I reached out to the manufacturer, I asked if I should use a battery maintainer. All they told me was to monitor voltage after I finished driving for the day and make sure that the resting voltage was at least 12.85 volts.
A few months ago, I replaced the one-and-a-half-year-old factory Honda EFB (made by Clarios) with an Odyssey H5 AGM on my '24 Civic. Why would I replace such a newish battery? I thought I saw battery acid leaking. Plus, I wanted parking mode on my dash-cam to last as long as possible.
Everything was fine until I started to experience difficulty starting my car. And, based on the volt readings from my OBD2 gauge, my battery dropped to 10.8 volts when off. Rather worryingly, voltage would fluctuate in the 14-volt range. I've already warrantied the battery, and the replacement is behaving as expected.
The Civic is driven almost every day on a 40+ mile commute (weekends are mostly short errands). While I know Honda's alternator adjusts output voltage based on load, this page by Varta (owned by Clarios) says swapping an EFB for an AGM is perfectly fine. Based on my OBD2 gauge (it may not be the most accurate, but it's what I have), with my foot on the gas pedal under light loads, voltage is 12.4 volts. When the car senses higher loads, the voltage is 14.4-14.6. It only sees that voltage when the climate control is on high, when the lights are on, or when I'm coasting. I know European cars require a battery registration when swapping to avoid overcharging, but I haven't been able to find anything similar for the Civic. The only thing I could find was resetting the voltage monitor through HDS or a similar diagnostic tool.
The electronic accessories installed in my car that may be correlated:
- Idlestopper: only enabled when accessory power is engaged
- Dashcam: hard-wired and set to turn off when it drops below 12.2 Volts
- Fog light harness: Positive wire connected to positive battery terminal; though fog lights only work when the car is on.
- AAWireless adapter: only works when the car is in either accessory mode or full power.
- P3 Gauge: Plugged into the OBD2 port
- Non-electronic: Terminal protectors (both felt and spray); I highly doubt these cause an issue.
Unless I'm dumb, and my OBD2 gauge always plugged into the port may be contributing to parasitic drain.
Any thoughts before I go ahead and dismiss this as a bad battery? When I reached out to the manufacturer, I asked if I should use a battery maintainer. All they told me was to monitor voltage after I finished driving for the day and make sure that the resting voltage was at least 12.85 volts.
