Been tinkering a bit with portable pumps for use with Tubliss and
don't have any reliably satisfactory solutions. Most small electric
pumps are wretchedly constructed. I had hopes for an Airman Tour, but
it broke (literally, right through the crank/cylinder frame) after a
few cycles of beadlock bladder filling. Granted, I was running it to
120 PSI, but it's likely have failed a little later at 100 PSI. As a low
pressure pump it's rather nice, with an accurate gauge and small size.

The neatest, smallest 12V pump is the Dynaplug Micro. It's very nicely
made, but suffers from the same weak crankframe bracing as the Airman.
It might be stronger, and will certainly go to 120 PSI, but I'd not want
to stress it that much if I really needed it to work. It's very small if
you remove the unneeded accessories. The air hose is stiff and the chuck
leaks on disconnection, but most do. 

The longest-surviving 12 V pump I've used is an unknown brand marked only
"Coido" on the crank and conrod. It has a plastic crankcase, but it's well
braced and has shown no sign of trouble despite many sessions of rimlock
bladder inflation to 125 PSI. Came from a big box store and cost about $10
maybe fifteen years ago. 

The need for over 100 PSI points to road bicycle pumps, and that may
be the most realistic answer for topping up. I'd surely not want to
fill a rear tire from empty that way, however.

One pump that seems to work is a Specialized WindPipe, a dual cylinder
tire/shock pump for mountain bicycles. The low pressure section will
fill a tire quick as any hand pump, the high pressure section will give
well over 100 PSI with relatively low effort. Best of all, the air chuck
does not leak at all on disconnection, so the pressure you pump to is
the pressure you keep. Alas, I think it's discontinued, and somewhat
clumsy to use.  If you find one try it. 

I'm still looking for a compact, well-crafted 12 volt tire pump that can
_actually_ produce 125 PSI without breaking.