I don't think it would be great for this application, and may not work at all in the way you want. The output (as Tom said) is very likely to be the same voltage as the input. If you have a charger with too high of a voltage output, you'd basically be just cutting down on the current capability of the charger but still having the output voltage you don't want. You may even have a bit higher output because the load would be less overall. Inherently by design, a PWM controller is a lot closer to an average current control than a peak voltage control.
You would likely also get a lot of electrical noise in your DC system. 16 kHz is about the same frequency as the whine of old TVs and can be quite annoying to younger ears.
Both of these could probably be helped, at least to some extent, with an appropriate filter on the output. Still, on the whole, I don't really think this device is a good fit for the application.
