Milled out battery space --> how much carbon to compensate?

As you can see in the pictures, I milled out a battery space out of an kinda old Sector9 downhill deck. I milled out 4 layers of the 8 but because of the concave “only” the part that is blue is really that deep.

I do have carbon and epoxy and I am intending to support the structure like in this turorial: tutorial by

My question is: How many layers of carbon are required to make it safe again to ride on?

Also: Should I add another layer over the whole underside of the deck, too? If so, I would do it as described here: hand lay carbon tutorial

What are your thoughts / experiences / suggestions?


Carbon is conductive so be careful putting batteries inside

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yes, thanks for the reminder. I will put velcro between carbon and the battery

Just put a layer of thin fiberglass on the carbon, imo a better solution

You could also line with fish paper, very nice looking deck. What battery configuration are you fitting in the space?

It is a 10S4P battery

I will try the fiberglas over carbon solution

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Carbon, being conductive, also blocks radio signals, so beware of that with your receiver placement.


I have found that 4 layers are enough for me. Every person is going to be slightly different.

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What fabric you use will determine how many layers you need. As an example, a 200gsm fabric would require 4 layers to do what 1 layer of 800gsm would do. This is relative though, and there is the possibility that 4 layers of light fabric would be more rigid than a single layer of heavy fabric. Additionally, the term “safe to ride” depends on how fast you wanna go.

Do you mean 4 layers just in the battery compartment or over all of the deck?

Thank you guys for your help!!! I am planning to start in a few days…