Battery & Charging System


The battery and charging system is largely taken from the Tesla Model S. The battery was chosen due to the high energy density and the modular nature of the pack allows easier integration into the Rolls Royce frame, than, for example, the Model 3 pack.


Component Location

1. HV battery 2. 20 kW onboard charger 3. HV Junction box 4. DC-DC Converter 5. Inverter 6. LV battery 7. Motor 8. AC/DC Charge Port

Component Schematic

(Courtesy Tesla Motors)

Component Descriptions

HV Battery

The HV Battery is located in the space vacated by the original V8 internal combustion engine. The purpose of the HV Battery is to provide power to drive the car and run all the accessory systems. It is the primary energy source for the vehicle. It supplies direct current to the drive inverter for propulsion, and to the DC-DC converter for support of the 12V electrical system. The DC-DC converter also functions as a high voltage junction block, distributing current from the HV Battery to the A/C compressor, coolant heater, and cabin heater.

The Battery also contains B+ and B- contactors, a current measuring shunt, and a 630 amp fuse.

TeslaRR uses battery modules from Tesla Model S/X battery packs. All Model S battery options leverage the same enclosure and internal components, but vary the cell or module count to achieve different energy capacities. All configurations use lithium-ion 18650 cells.

  • 60 kWh: 26kg * 14 modules/pack, 6 bricks/module, 74 cells/brick = 6216 cells, 364kg of modules. (209 Wh/kg)

  • 90kWh: 26kg * 16 modules/pack, 6 bricks/module, 74 cells/brick = 7104 cells, 422kg of modules. (209 Wh/kg)

  • 100 kWh: 30kg * 16 modules/pack, 6 bricks/module, 86 cells/brick = 8256 cells, 480kg of modules. (213 Wh/kg)

The modules are re-arranged to fit in the engine compartment and are mounted to the front subframe using a custom battery cage.

Using the more widely available 90kWh Tesla model S modules, each containing 444 3.4Ah 18650 cells (6s74p) gives ~200 miles range. The larger packs contain 516 cells (6s86p) and provide a range of ~230 miles.

Note that the larger pack is required to provide enough power for the performance motor at a 4C discharge rate

Lithium-ion cell condition management is very important for safety and battery longevity. Each module has its own Battery Monitor Board (BMB), which monitors each brick's voltage and samples temperature from four points within the module. The BMBs report this information to the Battery Management System (BMS) via an internal communication bus. The BMS then uses this information to manage HV Battery temperature and SOC, and controls the main contactors. . The BMS communicates on the powertrain (PT) CAN bus. To maintain nominal Battery temperature, it makes requests of the thermal management system. To manage SOC, it communicates with the master charger, charge port, drive inverter, DC-DC, gateway module, and off-board charging connectors.

Charging System

  1. 20 kW onboard charger

  2. HV junction box

  3. DC-DC converter


The charging system, comprising the onboard charger, the DC-DC converter and the HV junction box, are colocated behind the rear seat in the space previously occupied by the fuel tank.

The HV Battery must be recharged on a regular basis by connecting the vehicle to an external power source.

NOTE: If both the 12 volt battery and the HV Battery become fully discharged, the 12 volt battery must be charged first, so that the charge port door can be opened.

NOTE: The HV Battery can only be charged if its temperature is within a predetermined range. If Battery temperature goes outside the normal operating range, the charge current might be reduced or charging might be completely inhibited until the temperature returns to normal.

The vehicle should be connected to a charging device whenever it is not in use. This ensures that the vehicle battery is always fully charged and the vehicle is ready for use.

TeslaRR is fitted with a Combined Charging System (CCS) Combo 2 connector, which is backwards compatible with the Type 2 connector. Adapters are available that can plug into the following sources:

  • 240 volt wall outlet

  • 110 volt wall outlet

  • Public charging stations (J1772)


The 20 kW onboard charger is compatible with these input ranges:

  • 85 - 265 V

  • 45 - 65 Hz

  • 1 - 80 A

  • Peak charger efficiency of 92%

While recharging from an external AC source, the onboard charger converts the AC to DC and controls the flow of charge current to the HV Battery depending on existing conditions, to ensure the HV Battery is charged at the proper rate and to the correct SOC.

NOTE: No current flows through the onboard charger during DC charging. However, the master charger is still crucial to the process, as it controls the fast charge contactors inside the HV Junction Box.

The temperature of the onboard charger is regulated by the thermal management system, which controls the flow of coolant through the powertrain cooling circuit. For more information, refer to the Thermal Management section.

High voltage junction box

  1. High voltage battery

  2. B- contactor

  3. B+ contactor

  4. High current bus bars

  5. 2 x 50 Amp fuses

  6. Charge port

  7. To DC/DC converter

  8. 20 kW charger

  9. 100 Amp fuse

  10. Low current bus bars

  11. Noise filter

  12. Drive inverter

The HVJB allows current to flow between the HV Battery, drive inverter, DC-DC converter, onboard charger, and the charge port. An HVIL switch on the lid should disable the HV system when the lid is removed, but always follow the vehicle electrical isolation procedure and verify that no voltage is present before beginning work. The HVJB contains the fast charge contactors, which are controlled by the master charger, that close to create a direct link between the charge port and the HV bus. The contactors are normally open, and only close while supercharging to allow current to flow directly to the HV Battery. The HVJB contains 3 fuses: a 50A fuse on the DC positive output from each charger, and one 100A fuse on the DC positive supply circuit that goes to the DC-DC converter. If no slave charger is installed, the connectors are inserted into a holding fixture, and the vehicle harness connector is plugged into the dummy connector on the side of the HVJB, so that the HVIL and CAN circuits are complete.

DC-DC Converter

The DC-DC converter is connected to both the 12V electrical circuit and the high voltage circuit. Its purpose is to convert Battery high voltage (350- 400VDC) to 12-13 VDC to power all of the vehicle’s low voltage requirements, and to maintain the charge of the 12V battery. It also serves as a HV junction box to distribute HV current to the A/C compressor, coolant heater, and PTC heater. When the vehicle is on and the contactors are closed, the DC-DC supplies the current necessary to operate the entire 12V electrical system. When the vehicle is off and the BMS is in standby mode (contactors open), if the 12V battery voltage drops below 12.3V, the gateway module requests the BMS to enter support mode. In this mode, the BMS closes contactors and supplies current to the DC-DC converter, which in turn maintains the 12V battery within its nominal SOC range.

The temperature of the converter is regulated by the flow of coolant around the battery coolant loop. For more information, refer to the Thermal Management section.

12V Battery

The 12 volt battery is located under the boot floor on the right-hand side. The purpose of the 12V battery is to provide an energy source for the 12V electrical system when the HV system is inactive. In the event of a HV system or DC-DC converter failure, it acts as an energy reserve for the entire 12V system, but most importantly to critical vehicle control and safety systems. These include:

  • Exterior and interior lighting

  • Wipers and washers

  • Door handles and latches

  • Electric Power Steering

  • Anti-lock braking and stability control

  • Instrumentation

It is a maintenance-free lead acid battery and is kept charged by power from the HV Battery, through the DC-DC converter. (Note that the use of a lead acid battery means that it can still be charged by the HV battery, even when the temperature drops below 0°C).

Charge Settings and Devices

The charge settings screen is accessible on the Vehicle Controller touchscreen by touching the battery icon in the top status bar, or by opening the charge port door. If the charge settings screen has been dismissed, bring it back by touching the battery icon again.

CAUTION: Repeated use of the MAX RANGE setting reduces the life of the vehicle battery.

  • Touch to select the desired charge level:

    • STANDARD This setting provides the best option for vehicle charging time and vehicle range. The HV Battery is charged to approximately 90% of its total capacity, which helps to maximize Battery life.

    • MAX RANGE This setting charges the HV Battery to maximum capacity. The vehicle can then achieve the maximum range possible on a single charge.

Charging current is automatically set to the maximum value available from the charging device attached, unless it has been previously reduced to a value lower than the maximum available. The current level can be changed using the up and down arrow keys.

NOTE: Charging current cannot be set to a level that exceeds the maximum available from the charging connector.

Reducing the current level prevents the possibility of overloading the wiring circuit. This is particularly useful if you are charging from a domestic wall outlet that might be on a shared circuit with other connected equipment, or is rated lower than the current capacity of the charging connector.

A reduced charging current is automatically remembered the next time the vehicle is connected to a charging cable. If you are charging at a different location, you must manually change the charging current for that location.

NOTE: Reducing the charging current increases the time required to charge the vehicle.

Charging Time

Charging times vary based on the voltage and current available from the power outlet. Charging using a 40 amp, 240 volt outlet provides approximately 31 miles of range per hour of charge. Charge time also depends on ambient temperature and the vehicle’s HV Battery temperature. If the Battery is not within the optimal temperature range for charging, the thermal management system heats or cools the Battery before charging begins.

Battery Life

On average, the HV Battery discharges at a rate of 1% per day. Situations might arise where the vehicle is unplugged for an extended period of time. In these situations, keep the 1% in mind to ensure the Battery has a sufficient charge level. For example, over a two week period (14 days), the Battery discharges by approximately 14%. Discharging the Battery to 0% can permanently damage the Battery.

To protect against a complete discharge, the vehicle enters a low power consumption mode when the charge level drops to 5%. In this mode, the Battery stops supporting the onboard electronics to slow the discharge rate to approximately 4% per month.

Once this low power consumption mode is active, it is important to plug the car in within two months to avoid Battery damage.

NOTE: When the low power consumption mode is active, the auxiliary 12V battery is no longer powered and can fully discharge within twelve hours. In the unlikely event this occurs, the 12V battery must be jump-started or replaced before the the vehicle can be charged.

Charge Current Flow

The vehicle can be charged using either an AC supply or a DC supply. The path that current follows once it enters the HVJB is different for AC and DC charging. DC charging is faster because it can supply nearly three times as much current as AC can.

The vehicle recognizes when an AC charge source is connected using CAN communication with the BMS. When charging from an alternating current (AC) source, current flows from the source through the connector to the charge port. From the charge port, it passes to the HVJB and is then routed by bus bars to the onboard charger. The charger converts the AC to DC and supply current to the HV Battery.

If the car is connected to a HPWC, output is doubled to 20 kW. As battery SOC increases, charging current tapers off.

The vehicle recognizes when a DC charge source is connected using CAN signal supplied from the Supercharger to the BMS. This signal takes the form of a 5% duty cycle waveform on the pilot signal (generated by the Supercharger). The BMS sends a CAN message to the master charger, which then closes a set of contactors inside the HVJB.

Current flows from the Supercharger through the connector to the charge port. From the charge port, it passes to the HVJB and is then routed through the closed contactors to supply DC to the HV Battery.

The Supercharger increases its voltage and current output to charge the Battery with up to 90 kW, which tapers off as the Battery state of charge increases.

Regenerative Braking (Regen)

Regenerative braking, or regen, is the conversion of the vehicle’s kinetic energy into electrical energy stored in the HV Battery, where it can be used to drive the vehicle. The regen system is integrated within the motor and drive inverter and is designed to charge the Battery. Control of the system is managed by the vehicle firmware and the drive inverter.

Regen typically creates an effect similar to the engine braking that is experienced when releasing the accelerator in a car with a manual transmission.

When the vehicle is decelerating, the kinetic energy of the car continues to turn the induction motor’s rotor. The firmware applies an AC field that is less than the synchronous frequency for that speed. Hence, current flows from the motor through the inverter and into the Battery pack. This can amount to tens of kilowatts flowing into the Battery, although the charge decreases with decreasing vehicle speed.

The amount of regen braking available depends on many factors, including, but not limited to: vehicle speed, battery state of charge, operating temperature, and driver’s preference. Regen can be set on the on the Vehicle Controller touchscreen.