The complete Tesla Model S 85kWh battery pack weighs approximately 1,200 lbs (544 kg). However, DIY power wall builders and off-grid integrators rarely use the full pack. Instead, they salvage individual 5.3 kWh modules, which weigh exactly 56 lbs (25.4 kg) each. Understanding the Tesla S battery weight and physical dimensions is the first critical step in designing a structurally sound, electrically safe 48V energy storage system.
Tesla Model S Battery Weight and Module Specifications
Tesla utilized different cell densities and module configurations across the Model S production run. When sourcing salvage modules, you will typically encounter the 85kWh, 90kWh, or 100kWh variants. The physical weight of these modules dictates your racking requirements, while the internal cell chemistry dictates your Battery Management System (BMS) parameters.
| Pack Variant | Module Capacity | Cell Chemistry | Cells per Module | Module Weight | Nominal Voltage |
|---|---|---|---|---|---|
| 85 kWh | 5.3 kWh | NCA (18650) | 444 (74p6s) | 56 lbs (25.4 kg) | 22.2V |
| 90 kWh | 5.6 kWh | NCA (18650) | 444 (74p6s) | 58 lbs (26.3 kg) | 22.2V |
| 100 kWh | 6.1 kWh | NCA (18650) | 516 (86p6s) | 62 lbs (28.1 kg) | 22.8V |
| Plaid / Structural | N/A (Single Unit) | NCA (4680) | N/A | ~1,100 lbs (Total) | ~350V |
For a standard 48V nominal DIY power wall, the 85kWh modules are the most common. Because each module is a 6-series (6s) configuration, wiring two modules in series creates a 12-series (12s) bank. This yields a nominal voltage of 44.4V and a maximum charge voltage of 50.4V, which aligns perfectly with the DC bus requirements of most 48V hybrid inverters.
System Architecture and Sizing Math
A properly engineered power wall requires a clear source-to-load pathway. Here is the standard system block description for a Tesla module-based setup:
System Block: Solar Array / Grid AC → MPPT Charge Controller / AC Coupler → 48V DC Bus → Battery Bank (Tesla 12s Modules + BMS + Class T Fuse) → Hybrid Inverter → AC Load Panel.
When sizing your battery bank, you must account for inverter efficiency and the Peukert effect. While Peukert’s law heavily penalizes lead-acid batteries at high draw (exponent ~1.3), lithium-ion NCA cells exhibit a Peukert exponent of roughly 1.02 to 1.05. We will use 1.03 for our conservative sizing math, alongside a 93% inverter efficiency rating.
Sizing Example: 5kW Continuous Load for 4 Hours
- Target AC Load: 5,000W
- DC Power Required: 5,000W / 0.93 (inverter efficiency) = 5,376W
- Base Current Draw: 5,376W / 44.4V (nominal) = 121A
- Base Ah Required: 121A × 4 hours = 484Ah
- Peukert Adjustment (1.03): 484Ah × 1.03 = 498Ah usable capacity required
A single 12s string of 85kWh modules provides roughly 238Ah. To meet the 498Ah requirement without over-stressing the cells, you need two parallel strings (four modules total), yielding 21.2 kWh of raw capacity and 476Ah at 44.4V. This keeps the draw per string at a comfortable ~60A.
Series vs. Parallel Wiring and Operational Limits
Understanding the consequence of series versus parallel wiring is non-negotiable when mixing high-capacity modules.
| Wiring Method | Consequence for Voltage (V) | Consequence for Capacity (Ah) | Primary Use Case |
|---|---|---|---|
| Series | Voltages add (22.2V + 22.2V = 44.4V) | Ah remains identical (238Ah) | Stepping up to 48V inverter compatibility |
| Parallel | Voltage remains identical (44.4V) | Capacities add (238Ah + 238Ah = 476Ah) | Increasing runtime and lowering C-rate per string |
Crucial Warning: Never parallel strings that have mismatched cycle counts, differing internal resistance, or unbalanced state-of-charge (SoC). If a 40V string is paralleled with a 48V string, massive equalization currents will flow, potentially melting busbars and causing immediate thermal runaway. Always top-balance all strings to exactly 4.2V per cell before closing the parallel contactor.
Charge and Discharge Limits (C-Rates and DoD):
Tesla NCA modules are capable of 1C continuous discharge (238A per module) in a vehicle. However, in a stationary power wall without active liquid cooling, you must derate this. Limit your continuous discharge to 0.5C (119A per string) and your charge current to 0.2C (47A per string). For Depth of Discharge (DoD), configure your BMS low-voltage cutoff at 3.0V per cell (10% remaining) and your high-voltage cutoff at 4.15V per cell (90% full). This partial cycling will extend the NCA calendar life from ~1,000 cycles to well over 3,500 cycles.
Inverter Sizing, Structural Framing, and Fire Safety
For a 21.2 kWh bank (four 85kWh modules), a 5,000W to 8,000W 48V hybrid inverter (such as the Victron Quattro 48/5000 or a Sol-Ark 8k) is the correct pairing. The inverter’s internal charger must be configured to output a maximum of 94A (0.2C across the 476Ah bank) to prevent overheating the internal cell bonds during bulk charging from a generator or grid.
Structural Framing for Tesla S Battery Weight
Four 85kWh modules weigh 224 lbs (101 kg) bare. Once you add 12-gauge steel Unistrut, copper busbars, BMS wiring, and Class T fuses, the total rack weight will exceed 275 lbs. Do not use standard wood shelving. Build your rack using welded 2x2 inch 11-gauge steel tubing or heavy-duty slotted steel angle, bolted directly into wall studs or anchored to a concrete slab. The modules must be supported from the bottom aluminum extrusion plate; never suspend them by the terminal ends.
By respecting the physical weight, adhering to strict NCA voltage limits, and calculating your loads with Peukert and efficiency factors in mind, salvaged Tesla modules remain one of the most cost-effective, high-density options for DIY off-grid energy storage available on the secondary market.
