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AGV & AMR Battery Sizing — How Big a Lithium Battery Does Your Robot Need?
Last updated: · Written by the Leolus Energy engineering team, Bangalore.
Read time: 8 min · Who this is for: robot makers, integrators and plant engineers specifying a lithium battery for an AGV, AMR or mobile robot
Start with the duty cycle, not the battery
The most common mistake we see in robot battery enquiries is a request for “a 48V 100Ah battery” with no duty cycle behind it. Two AGVs with the same motors can need packs that differ by a factor of four, depending on how they charge. Before talking to any lithium battery manufacturer for industrial robots, write down:
- System voltage the drive controller expects, with its minimum and maximum input.
- Average power over a real shift — drive, lift or arm, computer, sensors and lights — measured if possible, not taken from the motor nameplate.
- Peak power on acceleration, ramps and lifting, and how long it lasts.
- Charging plan — overnight only, opportunity charging at a dock between tasks, or battery swap.
- Working days per year and shifts per day, which set the cycle count.
Step 1 — Choose the system voltage
| Voltage class | LiFePO4 configuration | Typical use |
|---|---|---|
| 24V | 8S (25.6V nominal) | Small AMRs, cleaning robots, service robots, light tuggers |
| 48V | 15S or 16S (48–51.2V nominal) | Most warehouse AMRs and AGVs, mobile manipulators, heavier tuggers |
| 72V and above | 22S+ (custom) | Heavy-load AGVs and forklift AGVs — usually specified by the vehicle OEM |
Match the pack’s full-charge and cut-off voltages to the controller’s input range, not just the nominal figure. A 16S LiFePO4 pack reaches about 58V at full charge, which some “48V” controllers do not accept.
Step 2 — Work out the energy
Energy needed (Wh) = average power (W) × hours between charges ÷ usable depth of discharge
Use about 0.8 as the usable depth of discharge for LiFePO4 if you want a long cycle life, and add 15–20% margin for capacity loss over the pack’s life. Then divide by the nominal voltage to get amp-hours.
Step 3 — Check peak current
Peak current (A) = peak power (W) ÷ nominal voltage (V)
The pack’s BMS and cells must deliver that current for as long as the peak lasts without the voltage dropping below the controller’s cut-off. Robots that climb ramps or lift loads often need 3–5 times their cruise current for several seconds. A pack sized only on energy can trip on every ramp.
Worked example — a 48V warehouse AMR
These numbers are illustrative. Measure your own robot before ordering.
| Input | Value |
|---|---|
| System voltage | 48V (LiFePO4, 15S, 48V nominal) |
| Average power over a shift | 400W |
| Peak power (accelerating with load) | 1,800W for a few seconds |
| Shift length | 8 hours |
| Charging plan | Energy per charge | Pack size | Cycles per day |
|---|---|---|---|
| Overnight only (runs the whole shift) | 400W × 8h = 3.2kWh ÷ 0.8 = 4.0kWh | 4.0kWh ÷ 48V ≈ 83Ah → 100Ah with margin | 1 deep cycle |
| Opportunity charging (docks every 2 hours) | 400W × 2h = 0.8kWh ÷ 0.8 = 1.0kWh | 1.0kWh ÷ 48V ≈ 21Ah → 25–30Ah with margin | 4 partial cycles |
Peak current in both cases is 1,800W ÷ 48V ≈ 38A. The 100Ah pack delivers that easily. The 25–30Ah pack needs cells and a BMS rated for well over 1C continuous discharge, plus a charger and dock that can put the energy back in the time the robot spends docked.
The smaller pack is lighter, cheaper and frees space in the chassis. In exchange it does four times as many cycles, so cycle life decides the choice. At 300 working days a year, four cycles a day is 1,200 cycles a year. That is why opportunity-charged fleets almost always use LiFePO4.
LiFePO4 or Li-ion (NMC) for an industrial robot?
| LiFePO4 (LFP) | Li-ion (NMC) | |
|---|---|---|
| Cycle life | Longer — suits several cycles a day | Shorter |
| Energy per kg | Lower — heavier for the same energy | Higher — lighter and smaller |
| Thermal safety margin | Wider | Narrower; needs closer thermal design |
| Best for | AGVs, AMRs, tuggers, opportunity charging | Weight-sensitive robots, legged and aerial robots, compact service robots |
What the BMS has to do on a robot
- Talk to the controller over CAN or RS485 with a documented register map, so the fleet manager can read state of charge and plan charging.
- Handle partial charging without the cells drifting out of balance.
- Allow the peak current without nuisance trips, while still cutting off a real short circuit fast.
- Log faults so a field failure can be diagnosed.
- Survive vibration — floor joints and ramps shake a robot all day, which is harder on connections than an occasional knock.
FAQ — AGV and AMR Batteries
Have a duty cycle? We will size the pack with you.
Send the voltage, average and peak power, charging plan and the space available. See our industrial robot batteries, request a quote or message us on WhatsApp +91 96111 92399.