How is your HV battery holding up?

The topic of battery longevity comes up repeatedly here. We know Honda's policy is that a warranty replacement will occur only when the capacity drops below 66.6% of the nominal new capacity of 55 Amp-Hours within the 8 year (or 10 in California) warranty period.

The vehicle constantly monitors this capacity, but unfortunately, Honda chose to not make this available to us without a trip to the dealer who can obtain the number with specialized equipment.

In another recent thread, we had some discussions about how any owner could obtain a ball-park measure of battery capacity. It was proposed that you can gain a good feel for capacity by measuring how much energy is required to perform a 'full' charge on your vehicle (starting from an EV range of 0). As the battery degrades, less energy will be required to 'fill' it.

Some EVSE's measure and report detailed charging parameters (current, voltage, and total kWh). The EVSE supplied with the vehicle does not have this capability. Even many Level 2 EVSE's do not have smart interfaces for this.

If you know the output power from your EVSE, then you can just do a simple measurement of how long it takes to do a full charge. This can then be related to capacity. From our experimentation, I would like to propose the following procedure / criteria for battery evaluation. It intentionally covers two main cases... 1. The OEM charger (which everyone has), and 2. A Level 2 charger that operates at the full vehicle capability (240V, 30A - 7.2 kW). We have found that other types of EVSE units may not always yield a predictable charge rate. If you know what yours is, then this test criteria can be easily modified accordingly, but let's begin with the most common cases...

• Case 1 (OEM Level 1 EVSE):

Using your OEM charger, perform a full charge (starting with an EV range of zero).
Check your charging status at 8 and 10 hours to see if it has completed.​

• Case 2 (Level 2 EVSE, operating at full vehicle capability (240V @ 30A = 7.2 kW)):

perform a full charge and check the status at 80 minutes, and 100 minutes to see if it has completed.​

As I said, similar guidelines can be tailored to other charger capacities, but these are perhaps the most commonly used.

Any feedback would be appreciated. If anyone tries this, it would be nice to collect some reports that include mileage, charger type, and charge time (resulting capacity estimate). I thought about a 'poll', but I am not sure how to configure one with multiple dimensions.

PS - Experience has shown that with Level 2 charging, the 55 Ah rating corresponds to a full charge input of approximately 14.5 kWh. With Level 1, the nominal 55 Ah is more like 15.5 kWh.