I've run both a cm91 (90cc cub) and an Express with completely dead batteries, and never blown a headlight. The dead battery still work to limit the current passed to the light, and I like watching the bulb crawl its way to luminescence.
One question I've always had is why the Passport tanks are part of the body - a manufacturing decision? The old-style cubs (or maybe just my 67 cm91) have bolt-on tanks that look exactly like the frame tanks on Passports.
If you had a choice between the two, you'd always take the one that you can unbolt and clean, no?