Trek Bosch Range Boost 

Range Boost seamlessly attaches an extra 500Wh battery to compatible Trek electric bikes for up to twice the distance and time between charges. It’s ideal for riders who want to ride longer, commute farther, and adventure bigger.

this option is available for most of the Allant series bikes 

Range Boost adds extra for pulling a trailer or cold weather use

Range boost adds extra distance  in cold weather riding situations or  when using your e-bike as a tow vehicle , cold weather reduces the effective range on a lithium ion battery , having range boost keeps those big rides  an option .