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Britax Marathon G4 Convertible Car Seat, Onyx

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  • Base with safecell technology features safecells designed to compress in a crash, significantly lowering the center of gravity and counteracting the forward rotation of the child seat which normally propels the child toward the front seat
  • Harness ultra guard system (HUGS) provides resistance to forward movement in the event of a crash
  • Side impact protection comprised of deep side walls lined with energy absorbing EPP foam distributes crash forces, shields from vehicle intrusion, and contains the head, neck and body
  • Tangle free, five point harness distributes crash forces across the strongest parts of the body and provides a secure fit
  • Premium lower latch connectors for a quick and simple installation featuring a push button for easy release
  • Base with safecell technology features safecells designed to compress in a crash
  • Harness ultra guard system provides resistance to forward movement in the event of a crash
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1 new from $291.00
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Britax Marathon G4.1 Convertible Car Seat, Onyx
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Product Information

Color: Onyx
Technical Details
Item Weight19.5 pounds
Product Dimensions21 x 18.5 x 26 inches
Item model numberE9LQ91A
Target genderUnisex
Minimum weight recommendation5 Pounds
Maximum weight recommendation65 Pounds
Additional product featuresRemovable Seat Cushion
Number of items1
Best usesinfant car seats
Batteries requiredNo
Additional Information
Best Sellers Rank #12,880 in Baby (See top 100)
Shipping Weight22.2 pounds
ShippingCurrently, item can be shipped only within the U.S. and to APO/FPO addresses. For APO/FPO shipments, please check with the manufacturer regarding warranty and support issues.
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Product Description

Color: Onyx

Choose Only The Best in Safety For Your Child
Choose Only The Best in Safety For Your Child
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Britax Marathon Convertible Car Seat

Packed with comfort and safety features, the Britax Marathon convertible car seat is constructed to provide head safety through the use of Britax SafeCell Technology in the base, integrated steel bars, and energy absorbing Versa-Tether that work together to minimize head excursion and reduce the risk of head injury during a frontal impact. It offers a no-rethread and quick-adjust five-point harness and EZ-Buckle system for convenience when harnessing your child, and an easy-remove cover for quick clean-ups that also allows access to the belt paths from the front of the seat. The Marathon accommodates children rear facing from 5 to 40 pounds and forward facing from 20 to 65 pounds.

Choose Only The Best in Safety For Your Child – BRITAX Offers Head Safety Technologies For Advanced Protection

During a car crash, impacts with the front seat aren’t just dangerous – they can be deadly. BRITAX convertible car seats lower your child’s center of gravity to keep them safe, secure and away from front seat. The base of the Marathon includes SafeCell Technology comprised of SafeCells, an engineered material designed to compress in a crash. This compression lowers the center of gravity to counteract forward rotation of the seat, helping to minimize the risk of head injury during a collision. Located in the sides of the seat shell, integrated steel bars strengthen the connection to the vehicle and prevent forward flexing of the seat during a crash to reduce the risk of head injury. In the event of a sudden stop, the Energy-Absorbing Versa-Tether strap restricts forward movement and reduces crash forces with patented staged-release webbing and a two-point attachment. This webbing securely anchors the top of your child seat to your vehicle in either rear- or forward-facing positions.

No-Rethread Harness System and Comfort Features

The tangle-free, five-point harness allows for multiple height positions and can be adjusted without dismantling the harness or removing the car seat from the vehicle. Two buckle positions provide a snug, comfortable fit as your child grows. The seat's harness holders prevent the straps from getting in the way when you're putting your child in the seat, while the EZ-Buckle system maintains the harness buckle in a forward position to prevent your child from sitting on it when first entering the seat. Rear- and forward-facing recline options, as well as high-density foam cushioning, help your child relax on the journey. And the plush cover comes with matching comfort pads and an infant positioning pillow to keep children of all ages comfortable and secure. Product Information: The Britax Marathon is assembled in the USA and has a seven-year life. What's in the Box: Britax Marathon Convertible Car Seat, removable cover, comfort pads, infant positioning pillow, and user guide.

Base with SafeCell Technology

The seat is designed to keep your child safe and secure in a crash by compressing and significantly lowering the center of gravity, reducing the forward movement of the car seat.

Side Impact Protection System Diverts Crash Forces

The Britax Side Impact Protection system includes a rigid shell with deep side walls lined with energy-absorbing EPP foam to contain your child’s head and body and divert crash force energy while creating a barrier against possible intruding objects. This system also protects your child’s head and chest.

User-Friendly Features for Easy Installation

The Marathon takes the guesswork out of installing your car seat thanks to a range of convenience features. An anti-slip, contoured base grips and protects the vehicle seat. Premium lower Latch connectors make for a quick, simple, and tight installation, while the push-button allows you to easily uninstall the car seat. And easy-to-access, built-in lock-offs provide a secure installation when using the vehicle lap and shoulder belt.

Premium Latch Installation

Provides an audible click and an easy-pull strap to simplify installation as well as a push-button design for easy removal.

Integrated Steel Bars

Strengthen the connection to the vehicle and reduce forward flexing of the child seat during a crash.

Energy-Absorbing Versa-Tether

Features a staged-release tether webbing to slow the forward movement, reducing the crash forces reaching the child, and a two-point attachment to minimize forward rotation while anchoring the top of the child seat.

Customer Reviews

Our daughter hates riding in the car and fusses most of the time.
Amanda L Pyle
So easy to buckle in with the latch system, and to UNbuckle is a breeze as well, just press a couple buttons and voila!
Very comfortable, very easy to install, and it looks like very secure.

Most Helpful Customer Reviews

741 of 756 people found the following review helpful By MM TOP 500 REVIEWERVINE VOICE on January 16, 2014
Color Name: Onyx Vine Customer Review of Free Product ( What's this? )
This is how to choose which Britax car seat will work for you. It can be confusing but small differences matter.
Older seats have the numbers 55 and 70 which indicates maximum weight of the child, CS means Click and Safe snug harness indicator.

G4 is new line, accommodates seats up to 65 lb instead of 70lb.

From the simplest to the most advanced the new G3 models go:
Roundabout and Highway(up to 55 lb), Marathon, Boulevard, Pavilion and Advocate (all up to 65). First two are the base models with lower child weight and I would only consider the Marathon, Boulevard, Pavilion or Advocate.

Marathon has all of the features that the rest of the car seats have except for:
- true side impact protection (Marathon has Side impact protection, this the inside cushion around child's head, models above have extra head protection),
- super thick chest pads that are supposed to minimize forward movement during a crash, Marathon has a different version than the above models have, still ok though,
- Click& Safe indicator, you can hear the click in the other models, when kid is strapped correctly, I can hear several clicks before I can say my son is safely strapped, after every click I can check the pads on his chest to make sure they are not too loose and keep adjusting (also Boulevard misses that option).

The Advocate goes further and has a bulky addition in the head area for more safety, but it was too bulky for my VW. This the only difference between the Advocate and Pavilion.

Overall I rate the this car seat 5 stars.
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207 of 215 people found the following review helpful By Min214 on May 28, 2014
Color Name: Onyx Verified Purchase
I had always been happy with this car seat, but now I'm truly in love with it. My 16 month old daughter was in a car accident while in this car seat (rear-facing). The car was totaled, but she was 100% fine - not a scratch, not a bruise. She was asleep when the accident happened and when the door was opened to get her out of the car she simply smiled. Can't ask for more than that. As for the car seat, you would never know it was in an accident. It suffered no discernible damage. However, since you shouldn't use a car seat after it's been in an accident, I'm buying the exact same car seat again to replace it. After this experience, I will forever be loyal to the Britax Marathon G4 convertible car seat, and will always recommend it.
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116 of 124 people found the following review helpful By Busy mom of 2 on May 17, 2014
Color Name: Kiwi Verified Purchase
I purchased the Britax Marathon G4 along with the Recaro Proride based on reviews and price point. (I wanted to stay under $250) since Amazon offered free shipping and free returns I ordered both! I wanted to see what best fit my Honda Pilot. Here are my thoughts based on installing it rear facing.
*To recline this seat I had to lay it on it's back and really pull. To tighten the straps after my daughter was in the carseat was tricky as well. Buttons seem tight and not very "fast and friendly"- Maybe they'll loosen over time.
*straps have already tangled with just a few uses. Maybe this is operator error but frustrating all the same.
*Installing was a breeze. I wish there was a level built in the carseat like on my Chicco Keyfit- this just had a red line that says "put parallel with seat"- this was annoying to me. Some may have to put a towel under depending on curvature of seat.
*Head support is there but isn't overwhelming. I feel like she would be protected if we were in an accident but it's not too bulky that she can still turn her head and look out the window.
*The green material is much like I had on my infant carrier but the black is a plushy, thick material. If the whole carseat was this material is would be HOT!
*The base of the Marathon is thinner than the Recaro. I sit 3 across my seats (using a booster seat as well)and this was an added bonus. My middle child didn't feel squeezed between two carseats and my booster riding child could sit next to the baby if he wanted.
*As child grows, you don't have to unstrap straps and restrap through a higher setting. There's an easy pull bar and you just lift. Very handy. Especially if you might be sharing this carseat with multiple kids.
*Cover is washable!
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45 of 49 people found the following review helpful By NewBiker on February 27, 2014
Color Name: Onyx Verified Purchase
Looks great! fits into a small car with the narrow and elevated base. Recommend to somebody who has very small back seats
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24 of 26 people found the following review helpful By RBF on September 28, 2014
Color Name: Cowmooflage Verified Purchase
I have two young children and have tried and compared a lot of different seats. In the end, the britax marathon wins the award for the "next step" to the infant carrier seats. I think it gives the needed support for a young baby while also being a comfortable seat for an older toddler. I find that this seat offers fantastic safety features that go well beyond many of the comparable seats on the market.

For us, this seat did what we wanted (safe, functional, nice looking and comfortable) so we did not feel we needed to pay extra money for some of the additional features that the more expensive (Britax) models have. In fact, I think some of the newer features feel like an over-kill to an already great seat that is superior in safety!

The pros of the G4 to older Marathon models- the crotch buckle stays pointed out so you don't have to fish for it underneath your child. This is huge!

The cons or limitations-- this seat does sit up a bit higher than some of the comps (Diono, etc.,) I actually liked this as it feels better suited for babies and toddlers. However, I imagine that a 4-5year old might feel a bit baby-ish in the seat & the nice cushioned wings (although safe) do block the window view a bit. This was actually another reason I felt it wasn't worth paying extra money for the more expensive versions as I think we will probably upgrade to the booster/combo seat around 4 years old. If you are buying multiple seats for multiple kids and cars, you have to prioritize what is and what isn't important and if It doesn't add needed safety features, comfort or luxery.. I just don't see the point. then it starts to feel like just spending money to spend money.

So again.. great seat and the G4 does feel above and beyond others in it's class!
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