The battery instruction needs a model-specific answer
The carrier’s prohibited-items list explicitly bans separately carried lithium e-bike batteries. Moving the battery into a backpack therefore does not follow the published rule. Nor does putting a detached battery beside the folded frame establish that it is no longer being carried separately.
Brompton’s guide to travelling with an electric bike describes folding electric bikes as permitted luggage on Eurostar’s London routes, subject to the bag and size requirements. Later, under battery safety, it recommends removing the battery whenever transporting the bike without actively riding it. Its charging advice also suggests looking for designated station charging points; Eurostar’s own bike guidance prohibits charging a folding electric bike in its stations and on its trains.
These are different organisations giving instructions about the same journey. The public pages do not explain an agreed packing configuration that resolves the removal conflict for every Brompton model. They also do not establish when either instruction changed.
Do not improvise an attachment or disregard the manufacturer’s handling instructions to satisfy a reading of the carrier’s page. Ask Brompton about the safe transport configuration for your exact model, and ask Eurostar whether that configuration is accepted on your planned service. An earlier traveller’s successful boarding cannot confirm what your booking permits.
Measure the folded package for each leg
Eurostar’s folding-bike rules use different dimensions for different routes. To or from London, the folded bike must be no longer than 85 cm and inside a protective bag that covers the whole bike and can be sealed. Between Belgium, France, the Netherlands and Germany, a folding bicycle counts as ordinary luggage only within 75 × 53 × 30 cm.
Consider a hypothetical packed size of 80 × 50 × 28 cm for a London–Brussels trip followed by a separate Brussels–Paris Eurostar service. Its 80 cm length is below the London limit. On the continental leg, that same length exceeds 75 cm by 5 cm. Passing the first dimension check therefore leaves the second unresolved. This is an illustration, not a measured Brompton, a test journey or a guarantee of admission.
Measure what you intend to carry, including the cover, padding and protruding parts. Send both companies the model, battery arrangement, packed dimensions and actual services. A useful enquiry is: “My bike is [model], travelling on [services]. The manufacturer’s transport configuration is [description], with packed dimensions [measurements]. Is this arrangement accepted, and does the battery need any different handling?”
Keep the replies tied to that configuration. A size answer alone does not answer the battery question; a general statement that folding bikes are allowed does not confirm the dimensions for your onward leg. Resolve both before committing to a journey that depends on taking the bike.
