hello looking on treks site from what i can tell it looks like you will be able to convert with few issues. just make sure that battery fits in the triangle space, surely some shark batteries out there should fit.

https://www.trekbikes.com/us/en_US/bikes/mountain-bikes/cross-country-mountain-bikes/marlin/marlin-5/p/33136/

Bottom Bracket - VP BC73, 73mm, threaded cartridge

so u get the 68mm motor size and that fits easily in your BB, you will want to add a 5 mm shim to make it snug, tho idk where these motor shims are available

Thanks 1fitz for the info. I have confirmed that the BB Width is within the range that Bafang requires. The Bafang site describes that their systems work only with JIS-BSA bottom brackets that have a diameter of 33.5 - 35 mm. If the diameter of the BB is larger then you can get adapters from a 3rd party. I have not been able to find specific info online about the diameter of the Trek Marlin models BB diameter. So, to get an accurate measurement I would need to disassemble it to see if it is threaded and the correct size. I see that several people on this forum including Johnny himself have done conversions with these frames. I am hoping that one of them will let me know if they needed the adapters. I am making the assumption that it is likely that Trek would use the same standard BB for its frames in the same series. As for the battery, yes, I need to take measurements. I just found out that bends in the top tube might be standard for this years size small frames in this serious.

this is research youll want to DIY before making a decision. find your models BB diameter and make sure the motor fits, which is either 68,100,or 120 mm. Sizes in between 68-120 can be snugged with a shim. no one here knows unless theyve converted your model, if the motor or battery fits. measure the dimensions of your frame and make sure the battery can fit inside that.