Chalo
100 TW
In days of yore, I used a 30-something pound SLA pack on a Jandd Expedition rack and a 50-something pound SLA pack on a Blackburn Expedition rack. The Jandd rack had a bigger platform and thicker stays; the Blackburn rack had more numerous stays and better lateral bracing. Both of the racks survived to do other duty on other bikes, and both were pretty shaky when carrying hard mounted batteries on top. Most racks are plenty strong enough to carry the weight of a big battery pack, but lack the lateral stiffness to do it without wiggling from side to side. They're intended to carry big loads in soft bags, which supply damping and shock attenuation.
If you can break up your pack into halves, mounting them on the sides in panniers will make the bike ride better. No matter where you put the batteries, having some suspension for them (fabric bags on the sides, closed cell foam pad on the rack top, etc) will dramatically reduce the beating your rack takes.
If you can break up your pack into halves, mounting them on the sides in panniers will make the bike ride better. No matter where you put the batteries, having some suspension for them (fabric bags on the sides, closed cell foam pad on the rack top, etc) will dramatically reduce the beating your rack takes.