Very nice! What about the weight rating ? The side cases that were listed on Zero's website were rated for 10 pounds or so, is that a limit imposed
by the flimsy plastic case, or the mounting brackets ?
I'm sure the weight rating is for the rack - it's not very sturdy. On the other hand, manufacturer ratings for racks are always conservative but you have to use some judgement. Happy Trails makes a rugged rack designed against the DS/DSR but it fits an S/SR okay.
EDIT: I'm wrong, the E21 cases themselves are rated for 11lbs. But it's still conservative.
If you're really concerned with load because of chargers, read on (tl;dr: put a charger in the top case instead):
For the record, I've carried a 15lb Elcon 2500 in the E21 side case that Zero offers (and Ben Rich has carried one on each side hard-mounted to the racks). Its cooling fins were ground shorter by the previous owner for a project. I wrapped it in a towel to prevent the sharp corners from digging into the case plastics.
It is difficult to counterweight a heavy side load like that, and it will impact cornering response and suspension response. It will also demand that you double check the side rack mounting bolts over time and see whether the rack holds up the load over a year or more without sag.