Cylindrical NiMH battery, after 4 years + 30,000 miles

Just wanted to share some data on replacement High Voltage batteries that I purchased in 2019.

For the unfamiliar - Chinese companies make replacement HV batteries for the Prius that are cylindrical in form, which distinguishes them from OEM Toyota parts which are Prismatic (rectangular boxes). I bought some via a US importer, NewPriusBatteries, in 2019 for my ~185,000 mile Prius, for $1600.

I periodically recorded battery data over these 4 years and 30,000 miles of travel. Some sample graphs are below. Each graph shows data recorded over a few minutes -long trip, with elapsed time in seconds on the X axis. The first graph is an August 2019 trip, showing internal resistance of each of the 16 battery modules over a few minutes. The second graph is the same, but for a dataset recorded in July 2023. The third graph is the same idea but with voltages of each of the 16 modules, for a trip taken in August 2019. The fourth graph is the same but for July 2023.

I am not an expert, but I wasn't able to find significant differences in battery performance between 2019 and 2023. The internal resistance seems roughly the same as it was 4 years ago, as do the max and min voltages, and the patterns of change also seem about the same. Note the two trips have different data because I accelerated and braked at different times. Full data is available on https://treecricket.com/vehiviz , including car speed, battery current, battery temperature, and many other data points.

To conclude, I think the bet was a good one so far. Toyota OEM battery replacement, IIRC, had a warranty of something like 3 years and these have outlasted that already. Yet to be determined is if they will last over 12 years like the original OEM pack.









Data sources - BAFX II OBD reader, Android Torque Pro app, custom data processing python scripts and graphs with Plotly graph creation tool and javascript.

 

@spdracrm3

Around town with AC blasting and lots of idling I get about 40 mpg, on open highway (at 50-60 mph) i get high 50s mpg.

 

it would be pretty difficult to replicate the 2019 trips. but not totally impossible since the speed data + ambient temperature data is saved and a lot of them were on flat ground. (this data is on the website).

the thing im looking at on these two graphs is the highest delta-voltage between modules, which is stable at about 0.1, the ranges of the voltages, basically the same, and the range of the internal resistance, which is basically the same as it was 4 years ago. in other words, the car still runs and the batteries are not acting completely bizarre, which was the initial fear going in back in 2019, when it was all a complete unknown.

an interesting test might be to find some EV-mode pulls i did back then and see if i can replicate.

 

oops ok , so around town AC blasting in 105 F heat its actually been 30 mpg lately. . . . . this is like stop and go 40mph city streets with 0 highway travel , and a bunch of idling at park in the parking lot waiting for stuff to happen....