Charging Robot Fleets

Choose a charging strategy for your shifts

Fleets usually charge in one of three ways: short top-ups during gaps in the work, scheduled charging in quiet periods, or swapping a flat battery for a charged one. The right mix depends on your shift pattern and how much idle time vehicles have. Vehicles on a single shift may charge overnight, while round-the-clock fleets need charging folded into the work itself or spare capacity to cover it. Ask each maker to model a full day of your workload, showing battery levels across every vehicle and the number of chargers needed. Place chargers where vehicles queuing for them will not block busy routes or fire exits.

Ask which battery standard applies

Many mobile robots and guided vehicles use lithium-ion batteries, which bring their own safety requirements. IEC 62619:2022 sets safety requirements for secondary lithium cells and batteries used in industrial applications, and lists motive uses such as forklift trucks and automated guided vehicles alongside stationary ones, while road vehicles are dealt with elsewhere. Ask each maker whether its battery packs are tested to IEC 62619 or another recognised standard, who made the cells, and what the battery management system does when it detects overheating or a fault. Get the answers in writing, because your insurer and fire engineer will want to see them.

Set up charging areas to the rules

Charging areas need planning, and lead-acid fleets come with the most explicit rules. OSHA's powered industrial trucks rule, at 29 CFR 1910.178(g), requires facilities for flushing and neutralising spilled electrolyte, for fire protection, for protecting charging apparatus from damage by trucks, and for adequate ventilation to disperse fumes from gassing batteries. OSHA's eTool on electric trucks adds that charging should happen in a designated area and lists an eyewash able to provide a 15-minute flow. Robot docks spread across a floor raise similar questions on a smaller scale, so record how each charging point is protected from impact and kept clear of stored goods.

Plan for lithium-ion fire risk

Lithium-ion packs fail differently from lead-acid ones. OSHA's lithium-ion battery safety fact sheet says thermal runaway can be identified by a rise in battery temperature, venting of gas, vapour or smoke, or fire. It recommends storing batteries in dry, cool locations, limiting the quantity stored, following the manufacturer's instructions for charging and maintenance, recycling spent batteries through designated facilities, and preparing an emergency response plan with training for responders. Apply that to a robot fleet: quarantine damaged or swollen packs, keep spare batteries in a designated area away from combustible stock, and agree with your fire service how they should tackle a burning robot or charger.

Sources and further reading

• IEC 62619:2022 Safety requirements for secondary lithium cells and batteries, for use in industrial applications — International Electrotechnical Commission (IEC).
  Safety requirements for industrial lithium batteries, with forklifts and automated guided vehicles among listed uses.
• Lithium-ion Battery Safety (fact sheet) — Occupational Safety and Health Administration (OSHA).
  Workplace guidance on lithium-ion hazards, thermal runaway signs, storage, disposal and emergency planning.
• Powered Industrial Trucks eTool: electric power sources and battery charging — Occupational Safety and Health Administration (OSHA).
  Practical checklist for battery charging areas for electric trucks, with the OSHA requirements behind it.

Common questions

How many chargers does a robot fleet need?

There is no fixed ratio. The number follows from battery capacity, charge rate and the hours each robot works between idle spells. Keep spare charging capacity in each zone so that a single faulty charger does not strand vehicles during a busy period.

Can I replace lead-acid batteries in AGVs with lithium-ion?

Sometimes, but only with the vehicle maker's approval. The battery, charger and battery management system must be matched, and the vehicle's safety documentation may need updating. Ask whether the replacement pack has been tested to a recognised standard such as IEC 62619.