Budget Battery Capacity Readout

Hi there. Long time lurker but haven't browsed in a while. This is an intriguing topic and got me curious to see what my capacity is. My guess o meter has been netting me 38 to 40 miles of ev range and I think it is because I live on a hill where I don't regen on the way down given I charge to full. I also don't have LRR tires. With that said, I think my capacity should be within expectation but wanted to check.

Before I invest in Vgate device, wanted to see if anyone in the southern California, orange county area wanted to meet up to test my battery and chat it up. Let me know... Just private message me. If not, no worries.

Lastly, BIG THANKS to all those that contributed to the effort.

 

Shockingly, my car, a 2019 Clarity with 52000 miles has a 53.8 ah battery. I’m still shocked. Was bought by a dealer from CarMax and flipped over to me.

IMG_1749 by Fe2_O3 posted Feb 2, 2024 at 4:44 PM

 

The battery capacity is only reset after a full (100%) charge starting from an SOC (state of charge) of less than 30%). If one has a 50 mile EV range (on the dash meter) after a full charge, a 30% SOC corresponds to about 11 EV miles left. Currently, I recharge our Clarity about five times a week to about an 85% SOC and the SOC rarely gets below 50%. We drive mainly on EV around our small town. We use HV on any trips longer than about 20 miles but such trips are rare (we have a gasoline powered car just for our longer trips, all well over 100 miles a few times a year). Once a year, or so, I let the Clarity battery run down to about a 20% and recharge to 100% SOC to reset the battery capacity. I started doing this just over a year ago with a new Level 2 charger. Before that, I had set the Honda Smart Charge to stop at 85% but at least once a month, Smart Charge would fail and the charge went to 100%.

Over the past 15 months, our battery capacity has went down from 50.06 AH to 49.96 AH. I think this is great. You can see the battery capacity data under user Leop. BTW, we bought the 2018 Clarity Touring in February of 2018. It was the first Clarity our local Indiana Honda dealer got.

 

I think my comments above about the battery capacity reset can be misinterpreted. I was speaking toward how the Clarity battery management system determines the battery capacity. Just like in laptop computer or cell phone, the battery mangement system measures the charge (coulomb counting) going into and out of the battery. To get the battery capacity (measured in amp-hours where an amp is a coulomb per second), the best way is to start with the battery at zero state of charge and end at 100% SOC. However, it is hard to start at zero battery charge as that hurts Li-Po batteries. But, if one knows the starting SOC, say X%, one can get the battery capacity by just normaizing the measured amp hours by 100%/(100%-X%). For batteries in general, one can estimate the SOC by looking at the open circuit votage. However, Li-Po batteries have a nearly constant OC voltage from 25% to 75% SOC which make it hard to estimate the SOC in that range. This is why one is asked to completely discharge (this gets the battery down to about a 10% SOC) a laptop or cell phone battery before starting a battery capacity measurement. The Clarity BMS works the same way and it is my experince that the Clarity BMS will take about a 30% SOC to enable a battery capacity measurement.

The other meaning of a Clarity battery capacity reset is when the Clarity BMS loses the battery capacity measure. Some say that this can happen when the Clarity has a some sort of a system failure. In that case, the battery capacity may be reset to the new battery capacity of about 55 AH.

I think that many higher than normal battery capacity values may be the result of the Clarity not being fully charged from an SOC of less than 30% for a long time. This can happen if a Clarity is recharged everyday but is not driven very far each day.

Leop

 

Thanks for that update. I also have disconnected the battery momentarily without causing a Battery Capacity Reset. This makes me continue to wonder what specific variables do cause that reset. I don't recall anyone on this forum specifically pinning that down.