Britax Marathon ClickTight vs Cybex Eternis S

Both are convertible car seats — here are their published manufacturer specs side by side.

This compares published manufacturer specs — not safety or fit advice. The seat's manual, your vehicle's manual, NHTSA's tools and a certified CPST are the fit-and-safety authority; always check them before installing.

Spec	Britax Marathon ClickTight	Cybex Eternis S
Stage	Convertible	Convertible
Narrow (3-across)	–	–
Extended rear-facing	–	✓
FAA-approved	✓	✓
Lightweight / travel	–	–

Britax Marathon ClickTight

5–65 lb

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Cybex Eternis S

4–120 lb

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As an Amazon Associate we earn from qualifying purchases, at no extra cost to you. Weight ranges are the manufacturer's published limits across all modes.

How they differ

the Cybex Eternis S lists extended rear-facing (a higher rear-facing weight limit, ~40-50 lb); the Britax Marathon ClickTight doesn't

Published limits

Mode	Britax Marathon ClickTight	Cybex Eternis S
Rear-facing	5–40 lb	4–50 lb · 17–48 in
Forward-facing harness	22–65 lb	22–65 lb · 28–49 in
Booster (with back)	—	40–120 lb · 44–57 in · 3+ yrs
Useful life	10 yrs from manufacture	—

Britax Marathon ClickTight: Rear-facing: 5–40 lb and 49″ or less. Forward-facing: 22–65 lb and 49″ or less (printed limits, same height cap both modes).

Cybex Eternis S: All-in-one (rear-facing → forward-facing harness → high-back booster; no backless mode found in manual). Forward-facing also requires at least 1 year old. Useful life is set by the printed "Expires On" date (no printed number of years in the manual).

Printed verbatim in the manufacturer's manual (Britax Marathon ClickTight User Guide (Canada, P03810500B) · Cybex Eternis S Owner's Manual); “—” = not published for that mode, “not yet sourced” = we haven't read that manual yet, not that the seat has no limit. How we source these →

Recall record

Britax — 22 on NHTSA's record · Cybex — 4 on NHTSA's record.

That is the record of the brand — not a verdict on these models. A recall names specific models and manufacture-date ranges, and a seat missing from the record is not "recall-free": check nhtsa.gov/recalls with the model and date of manufacture on your seat's label. Source: NHTSA, retrieved 2026-09-05.

Where to buy

Britax Marathon ClickTight

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Cybex Eternis S

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FAQ

What's the difference between the Britax Marathon ClickTight and the Cybex Eternis S?
The Britax Marathon ClickTight is FAA-approved for aircraft; the Cybex Eternis S is extended rear-facing, FAA-approved for aircraft. Both are convertible car seats.

Which is right for my car and child, the Britax Marathon ClickTight or the Cybex Eternis S?
That depends on your specific vehicle and child — this page compares published manufacturer specs only, not fit or safety. Check the seat manual, your vehicle manual, NHTSA's car-seat finder and ideally a certified CPST before deciding.

Citing these specs? Go ahead — published manufacturer data, last verified 2026-06-11. Copy a ready-made reference:

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