How to Size a Lithium Battery Pack for AGV and AMR Applications

AGV and AMR battery packs have different constraints from UAV or portable device batteries. The primary design drivers are cycle life and operational availability, not energy density or weight. A pack that degrades after 18 months of daily operation costs more than one that was correctly sized from the start.

The AGV Battery Sizing Problem

AGV sizing is not a back-of-the-envelope calculation. The variables interact in ways that produce expensive mistakes if you get them wrong.

AGVs run in shifts, often 16 to 24 hours per day across two or three shifts. The pack must support a full shift without opportunity charging, or handle partial recharging between shifts. Undersized packs stall mid-shift. Oversized packs add weight and cost without adding value.

Cycle life makes this harder. A pack cycling twice per day over three years accumulates more than 2,000 cycles. Chemistry selection and depth of discharge management must reflect that number from day one, not as an afterthought during the second year of operation.

Step 1: Calculate Energy Requirement

Step 1a: Determine Average Power Draw

Measure the actual draw in watts. If load varies across a shift, acceleration, lift cycles, idle periods, use a weighted average. Typical AGV power draw falls between 1 kW and 5 kW depending on payload and speed.

Do not use peak draw as your baseline. It will oversize the pack and inflate cost.

Step 1b: Determine Shift Duration and Charging Strategy

Know your charging strategy before you run the numbers. It can change the required pack capacity by 40–50% depending on shift structure.

Step 1c: Apply the Sizing Formula

Required energy (Wh) = Average power (W) × Shift duration (h)

That gives you the base requirement. Add 20–30% margin to account for:

• Depth of discharge limit, operating at 80% DoD rather than 100% preserves cycle life
• End-of-life degradation, size for what the pack will deliver at 80% of rated capacity, not what it delivers new
• Peak loads and auxiliaries, sensors, compute, actuators all draw current

Example:

• Average power: 2,000 W
• Shift duration: 8 hours
• Base requirement: 16,000 Wh
• With 25% margin: 20 kWh nominal pack capacity

Step 2: Choose Voltage and Pack Capacity

Voltage Selection

Common AGV pack voltages: 24 V, 36 V, 48 V, 72 V.

Higher voltage means lower current for the same power. Lower current means less heat in cables, connectors, and the BMS. 48 V is the most common choice in modern AGV and AMR platforms. 72 V is used for heavier industrial vehicles where higher power transfer is needed.

Choose voltage based on your drive system requirements first. Then size capacity to match.

Capacity Formula

Required capacity (Ah) = Required energy (Wh) ÷ Nominal voltage (V)

Example: 20,000 Wh ÷ 48 V = 416 Ah nominal pack

At 80% DoD, the usable capacity is 333 Ah. That is the number to verify against your shift duration at your actual power draw.

Step 3: Select Cell Chemistry for AGV

This is where AGV requirements diverge sharply from UAV or portable electronics.

AGV requirements are specific: 500 to 2,000+ cycles depending on shift intensity, discharge rates at or below 1C, predictable degradation, and operation in a temperature-controlled warehouse environment, typically 15 to 25°C.

Chemistry Comparison

The Recommendation

Cylindrical NMC cells, operated at 70–80% DoD, are the right choice for most AGV and AMR applications.

The reasons are concrete, not theoretical:

• 4–6× more energy density than lead-acid. A 20 kWh lead-acid pack weighs six to eight times more than the equivalent NMC pack. That weight affects AGV payload capacity and floor loading.
• Fast and opportunity charging. Lead-acid cannot support opportunity charging without accelerating degradation. NMC handles it correctly with a capable BMS.
• No maintenance. Lead-acid requires watering, equalisation charges, and ventilation. NMC cylindrical packs require none of that.
• Cylindrical format mechanical advantages. No cell swelling under cycling. Predictable thermal behaviour. Mechanical robustness under the vibration loads common in industrial environments. And no single-supplier dependency for cells, cylindrical 21700 cells are produced by multiple manufacturers.

DoD Management Is the Key Variable

The most effective lever for extending NMC cycle life is not chemistry selection, it is DoD management.

A pack managed at 70% DoD delivers meaningfully more cycles than one regularly taken to 100% DoD. For AGV applications cycling once or twice per day, a well-managed NMC pack can deliver three to five years of service life without replacement.

Build the DoD limit into the BMS configuration from day one. Do not add it later as a workaround.

For extreme-duty 24/7 operations with more than 1,500 cycles per year: define your cycle count requirement at specification stage and discuss it with your supplier before finalising the design.

Step 4: Plan for Cycle Life and Replacement

Cycle life planning is part of the sizing exercise, not a separate conversation.

Define the minimum acceptable capacity at end of service life. Industry standard is 80% of rated capacity. A 20 kWh pack at 80% end-of-life delivers 16 kWh. Check that 16 kWh still covers your shift requirement. If it does not, size up the initial pack.

For fleet operations, track state of charge per cycle across the pack's service life. Packs that are approaching end-of-life in a fleet context need to be flagged and scheduled for replacement before they cause operational failures.

Key decisions to lock in at specification stage:

• Size for end-of-life capacity, not start-of-life
• Set DoD limit in the BMS, 70–80% is the working range for cycle-intensive AGV applications
• Model the replacement schedule as part of the total cost of ownership, not as a surprise

What to Send Your Supplier

Use this checklist when requesting a quote or starting a design conversation:

• Nominal voltage (24 V / 36 V / 48 V / 72 V)
• Required capacity (Ah) or total energy (Wh)
• Average and peak discharge rate (amps or C rating)
• Shift duration and charging strategy (opportunity / between-shift / hot-swap)
• Physical envelope: max L × W × H and weight limit
• Operating temperature range
• Target cycle life and service life (years)
• Charging infrastructure: charger type, voltage, current available
• BMS requirements: CAN/UART communication, fleet management integration
• Certifications required (UN38.3, IEC 62133, CE marking)
• Volume: prototype / pilot fleet / production

The more of these you define before the first conversation, the faster the design process moves.

Decisiones clave: Resumen

Size for end-of-life, not start-of-life. Build degradation margin into the initial pack capacity. A pack that barely meets requirements when new will fail operationally by year two.

Use 70–80% DoD as your working limit. This is the most effective lever for extending NMC cycle life. It costs nothing to configure in the BMS and it can extend pack service life by 30–70% depending on cycle intensity.

Cylindrical NMC delivers practical advantages. 4–6× energy density over lead-acid. Fast and opportunity charging. No maintenance. Mechanical robustness in industrial environments. Cylindrical format cells also give you supply chain flexibility that proprietary formats do not.

The higher the cycle intensity, the earlier the conversation with your supplier. A 24/7 operation cycling two times per day is a fundamentally different design brief from a single-shift warehouse application. Define it at specification stage.

Dan-Tech Energy builds custom lithium-ion battery packs for AGV and AMR applications across Europe, from prototype to production. Browse our battery pack catalog, or use the ToolBox to configure your spec and get a direct sizing recommendation. Lead times start at 3 weeks from confirmed spec.