I have a laptop and sometimes I forget to turn off the inverter for
it. If I had extra capacity, I would be better off with that.

Would you be better of building a DC-DC converter for the laptop
instead of running DC-high voltage AC only to transform it back to
low voltage and rectify it again? If your charger uses a proprietary
connector instead of the typical barrel setup (or a "smart" battery
minder) maybe you could find a spare charger and hack it to accept
14.4V input...?

While it would be less convenient (building a new converter every time
you get a new laptop that takes a different voltage) I can't help but
think it would be at least a little bit more efficient...

--Glenn Lyford