How a fleet charges is not a procurement afterthought. It decides how large the battery has to be, how much grid and civil work a site needs, how a timetable is drawn and, in the end, whether a bus or truck is earning or parked. The choice usually comes down to two patterns: charge the fleet overnight at the depot, or top it up in short bursts between runs at terminals and corridor stops.
Neither is universally right. Depot charging is the simpler, calmer model and suits duties that finish the day inside a single battery. Opportunity charging buys uptime and smaller batteries for high-utilisation duties that cannot afford to sit. The deciding factor is often the cell: a chemistry that tolerates repeated fast charging makes the opportunity model viable where a slower chemistry would degrade.
This guide explains both patterns, the trade-offs across uptime, battery sizing, infrastructure cost and route design, why fast-charge-tolerant chemistry matters, and how the CCS2 power tiers map to each. It is written from what Ampinity builds and operates, not from a brochure.
Two ways to keep a fleet charged
Depot charging means the fleet returns to a base and charges while it is parked — usually overnight, usually at moderate power, often many vehicles at once. It is the pattern most operators picture first because it mirrors how a diesel fleet refuels: do it once, do it where the vehicles already sleep, and start the day full. The charging is slower by design, the hardware is simpler, and the timetable barely has to bend around it.
Opportunity charging means the fleet tops up in short bursts during the working day — at a route terminal, a layover, or a corridor stop between runs. Instead of one long fill, the vehicle takes many short ones at high power. The battery never has to hold a full day of energy because it is refilled before it empties. This is the pattern that keeps high-utilisation duties moving: a bus on a busy corridor or a truck on a freight route earns more by topping up in minutes than by returning to a depot for hours.
The two are not rivals so much as tools for different duties. The honest question is not which is better, but which the duty cycle asks for — and for many fleets the answer is a measured combination of both.
The trade-offs that actually decide it
Four variables move together when you choose a charging pattern. Pull one and the others shift.
Uptime is the first. A depot-charged vehicle is unavailable while it charges, so the depot has to be large enough to charge the whole fleet in the off-peak window. An opportunity-charged vehicle charges in the gaps it already has between runs, so it stays in service through the day — at the cost of depending on charging being available exactly where and when the route needs it.
Battery sizing is the second, and it cuts the other way. Depot charging asks the battery to carry a full duty cycle on one charge, which means a larger, heavier, costlier pack. Opportunity charging refills often, so the pack can be smaller — less weight, less capital, faster to charge. Infrastructure cost is the third: depot charging concentrates cost at one site with many moderate-power points, while opportunity charging spreads high-power points across terminals and corridors, each needing more grid capacity. Route design is the fourth — opportunity charging only works if the timetable has dependable top-up windows and the chargers sit where the route already pauses.
- Uptime: depot charging takes the vehicle out of service to charge; opportunity charging keeps it running by charging in existing gaps.
- Battery sizing: depot charging needs a full-duty pack; opportunity charging allows a smaller pack refilled often.
- Infrastructure: depot charging concentrates moderate-power points at one site; opportunity charging spreads high-power points across the network.
- Route design: opportunity charging depends on dependable top-up windows at terminals and corridor stops built into the timetable.
Depot vs opportunity, side by side
The table summarises how the two patterns differ on the dimensions a fleet operator weighs. Read it as a starting frame, not a verdict — the right answer depends on the specific route, climate and timetable.
| Dimension | Depot charging | Opportunity charging |
|---|---|---|
| When it happens | Overnight, while parked | In short bursts between runs, during the working day |
| Charge speed | Slower, moderate power | Fast, high power |
| Battery size needed | Larger — carries a full duty cycle | Smaller — refilled before it empties |
| Operational complexity | Simpler — one site, one window | Higher — depends on top-up windows on the route |
| Infrastructure footprint | Concentrated at the depot | Spread across terminals and corridors |
| Uptime impact | Vehicle out of service while charging | Vehicle stays in service through the day |
| Best-fit duty | Lower-utilisation, day finishes on one charge | High-utilisation, vehicle cannot sit idle |
| Chemistry demand | Tolerates a slower chemistry | Needs fast-charge-tolerant chemistry |
Why the cell decides whether opportunity charging works
Opportunity charging asks the battery to take a fast, high-power charge many times a day, every day, for years. Most chemistries resist that. Charge them too fast, too often, and they degrade — capacity falls, life shortens, and the economics that justified the smaller pack disappear. This is why a charging strategy cannot be chosen independently of the chemistry underneath it.
Japanese LTO (lithium titanate) is built for exactly this duty. It reaches about 80% of capacity in roughly 6 minutes, which is what makes a between-runs top-up short enough to fit a layover. It holds 20,000+ cycles at 70% capacity or better, so the repeated fast charging that opportunity duty demands does not wear it out the way it would a less tolerant cell. It uses the full 0–100% state of charge, so a system needs less installed capacity to deliver a usable range — reinforcing the smaller-pack advantage. And it operates down to −30 °C and is intrinsically safe, which matters when the chargers sit out on a corridor rather than in a controlled depot.
This is why Ampinity puts Japanese LTO on the duties that lean on opportunity charging — buses, trucks and LMVs — and why the bus and LMV ranges are specified around fast top-ups rather than a single overnight fill. The chemistry is what turns opportunity charging from a theoretical convenience into a dependable operating model for high-utilisation fleets.
- About 80% charge in roughly 6 minutes — short enough to fit a layover or corridor stop.
- 20,000+ cycles at ≥70% capacity — frequent fast charging does not exhaust it.
- Full 0–100% usable SOC — less installed capacity for the same usable range.
- −30 °C operation and intrinsically safe chemistry — suited to chargers out on the corridor.
CCS2 power tiers, matched to the duty
The charging standard across the Ampinity range is CCS2, and the power tier scales with the vehicle and the pattern it runs. The point of the ladder is that a top-up is only useful if it is fast enough to fit the gap the route gives it — so heavier, higher-utilisation duties draw on higher power.
For light vehicles and the 7 m city bus, CCS2 delivers 240 / 360 kW — enough for quick top-ups on cars, LMVs and short city duty. For 9 m and larger buses, and for heavy trucks, the tier steps up to 800 kW / 1.6 MW. At that power a megawatt corridor stop becomes a short pause rather than a lost shift, which is precisely what makes opportunity charging workable for freight on a long corridor.
The charging stations are manufactured in three configurations on a 1000 V DC system — 360 kW, 800 kW and 1.6 MW — with dynamic power sharing across nozzles, so one platform can serve a car hub, a mixed corridor and a high-throughput freight stop. Depot duty leans on the lower tiers feeding many points overnight; opportunity duty leans on the higher tiers placed where the route pauses.
- 240 / 360 kW: light vehicles, LMVs and the 7 m city bus — quick top-ups.
- 800 kW / 1.6 MW: 9 m and larger buses and heavy trucks — megawatt corridor stops as a short pause.
- Stations in 360 kW, 800 kW and 1.6 MW configurations on a 1000 V DC system, with dynamic power sharing across nozzles.
How to decide for your fleet
Start with the duty cycle, not the charger. Map the route as it actually runs — service hours, layovers, peak loading, climate and the kilometres between natural pauses. If the day finishes comfortably inside one battery and the vehicles sit overnight anyway, depot charging is the simpler, cheaper model and there is no reason to complicate it. If the duty is intense enough that taking a vehicle out of service to charge would break the timetable, opportunity charging earns its extra infrastructure by keeping the fleet running.
Most real fleets land in between: a depot base for overnight charging, plus opportunity top-ups on the route to extend the working day and shrink the battery. The bus range reflects this — Japanese LTO packs that charge in minutes at the supported power, with range per charge extended by opportunity charging across the Charging Network. The trucks follow the same logic, with ranges quoted per charge and extended on the corridor via megawatt opportunity charging.
The split is a route-design exercise, and it is worth doing properly because it sets the capital and the timetable for the life of the contract. The aim is not to maximise charging — it is to put exactly enough power in exactly the right places, so the fleet is charging when it would be idle anyway and running the rest of the time.
Charging stations and an operated network
Ampinity both makes the chargers and runs the network they sit on, so a fleet is not assembling a charging strategy from a chain of suppliers. The charging stations are manufactured in three configurations — 360 kW, 800 kW and 1.6 MW on a 1000 V DC platform with dynamic power sharing — covering depot hubs through high-throughput corridor stops. These are distinct from, and feed into, the operated Charging Network that runs along the national corridors.
The Charging Network is the operated layer: the stations Ampinity builds, deployed and run on the corridors, so opportunity charging has somewhere dependable to happen. Because the cells, the vehicles, the stations and the network are engineered inside one system, the charging logic is designed around the route rather than bolted on after the sale — and a fleet answers to one accountable company for the whole running cost.
For bus authorities and operators, this pairs naturally with the as-a-Service model: eBaaS for buses bundles the vehicle, energy, charging and maintenance on one bill, with depot and corridor charging included, so a city pays for uptime and a kept timetable rather than carrying the fleet and the charging infrastructure itself.