Battery

The battery weighs 25 pounds and a spare costs $4561. It is rated 1875 Wh. EM says it is 50.4 volts, which seems a bit unusual but is honest. A white paper provided by the BMS manufacturer reveals the battery is a 14S12P configuration (12 parallel groups of 14 series cells).

50.4 volts divided by 14 series cells implies 3.6 volts per cell. This is the nominal cell voltage. The extreme limits of the cell voltage are about 3.0 (safely depleted) to 4.2 volts (hot off the charger). See the section SoC Indicator for more information. Some quick arithmetic yields useful data:

14 * 12 = 168 total cells

1875 Wh / 168 = 11.16 Wh per cell

11.16 Wh / 3.6 V ==> 3100 mAh cell

The 3100 mAh value indicates either a really good 18650 cell or a mediocre 21700 cell. Those numbers refer to the physical size of the cell. For example, an 18650 is nominally 18 mm in diameter and 65 mm long. The trailing 0 indicates a cylindrical shape. I have not personally had a peek inside the battery, but the prior owner provided the next photo.

It appears there are two cells across the width of the battery. So each cylinder pair would be 2 * 65mm = 130mm (or 140mm for 21700 cells) long. Judging by the external dimensions of the battery box, I'm assuming they are 18650 cells. A website helped me identify the cells based on wrapper color, mAh capacity, and the black band at one end. I concluded they are probably Panasonic NCR18650A. These cells weigh 45.5g each, so 45.5 * 168 = 7.65 kg or 16.8 pounds for all the cells.

Due to constant improvements, these cells have been superseded by ones with a B-suffix rated for 3400 mAh. I was able to find an old data sheet on the exact cells used in the battery pack. The A-suffix cells are rated for a maximum continuous discharge rate of 2C (or 2 * 3100 mA). That's 6.2A per cell, and there are 12 cell groups in parallel, so a 74.4A maximum continuous discharge current. Assuming a nominal 54V battery voltage that's about 4 kW, continuously.

I found the new B-suffix (3400 mAh) cells offered at $8 each so, even paying full retail, there is considerably less than $1350 worth of cells in the pack.

ePure Race battery au natural

Battery Components

The blue block is a Hall current transducer. In one of the photos provided to me, it is clearly marked LEM HAAS 200-S. This unit has a nominal +/-200 amp rating and can make measurements as high as +/- 600 amps.

There are two small rectangles encased in heat-shrink tubing. The one with red and black wires is probably a linear voltage regulator. The one with only red wires appears to be connected across the discharge contactor, so is likely the controller precharge resistor. I'd be curious to know its resistance.

Because of the precharge resistor, I expected to always see full battery voltage on the Anderson connector, but that's not the case. However, when the battery switch is OFF there is a persistent approximately 2 volts at the Anderson connector (but it will only source about 0.4 microamps). This would seem to just be a leakage current and is a bit weird for something with a mechanical contactor.

That's not how the EM 5.7 battery precharge is wired. In it, I don't see a separate precharge resistor. I think it must be integrated inside the discharge contactor. There's also no voltage present at the Anderson connector when not discharging. I only notice 2 “coil wires” for the 5.7 battery, so maybe precharge is a different coil voltage than discharge?

The ePure battery is fastened much more securely into the chassis than the 5.7 (however it does take a bit more wrangling to get the connector clear of the chassis).

Shipping a Battery

Shipping a lithium-ion (ePure) or lithium-polymer (5.7) battery is a huge can of worms! They fall under the heading of hazardous material (HAZMAT) also known as dangerous goods.

There are some exceptions for small batteries if they are installed in consumer devices such as laptops, mobile phones, power tools, or the like. But generally speaking, shipping hazardous goods requires a special certification. The U.S. DOT and IATA (international) regulations require initial and recurring training for all persons involved in handling, documenting, or transporting hazardous materials.

United Parcel Service, for example, offers the appropriate training courses as webinars. To learn how to ship within the US and Canada, the course costs $600 and must be renewed every 3 years. To ship internationally too, the course costs $1000 and that certification is only good for 2 years.

Individuals must be trained if they classify, package, label, or complete any shipper's declarations associated with offering a hazardous material shipment to a courier.

As of 2021, the civil penalty for noncompliance is a fine of up to $83,439 per violation per day. If the violation results in serious illness, substantial property damage, or death, the fine increases to a maximum of $194,691 per violation per day.