A laptop in a storm

Instapundit has an interesting discussion about recharging your laptop or smart phone after a power blackout. Is is OK to use outlets at McDonalds, etc? But what really caught me eye was a comment by Johan Bakker who installs home generators:

there are still serious issues with generators and UPS [Universal Power Supply] units. Except for the largest and most-sophisticated generators, these two devices do not play well together... UPS makers have set very-narrow boundaries on the frequency input that their devices will tolerate before calling a fault. ... UPS makers use the disruption in frequency as a warning that utility power is going out [and switch to battery backup]

Most home generators cannot keep the power frequency stable to ± 0.5 Hz as required by UPS (and circuit breakers?). Bakker recommends inverters instead

for low-level charging needs, like phones and laptops, the best solution is a 12V auto battery and a miniature inverter. The battery can be charged in so many different ways (from a car, from a charger running off a generator, from a lawnmower, from a solar panel, the possible ways are endless) and even a small lead-acid battery (like a lawn-tractor battery) has more-than-enough capacity to charge many cell-phones and laptops before requiring a fresh charge.