Portable battery for charging?

[jephoto]

Hey all. .a couple weeks ago I was thinking "how can I charge my batteries while out & about "
Thinking that I. Any put everything on the car. Phone, iPad, RC, batteries.
Realized I have this Power Pack thing meant to Jump start a car, but also has an air compressor for tires AND- a 110 plug outlet as well as a USB port.
Cool.

So I started carrying it in the car and when I pull a battery (and let it cool) I can now charge it while flying my other batteries and lock up the car.
It does work- but has its limitations.
Doesn't like heat. On hot days can't close up the car & leave it. Not safe anyway.
And I'm finding that when it gets to about 50% - after charging 3-4 P3 batteries, it stops charging and give off a warning alarm.
So, long way around, but- are any of you using something better??
I know there are Inverter batteries designed to plug in professional camera strobes in the field. More robust than my $100 car jump start thing.

What have you all come up with??

 

[J0ck0]

my father-in-law and i have kicked this idea around quite a bit. i ended up purchasing a 750/1500w power inverter from Harbor Freight. i plan to connect it to a dry-cell car battery and put them both in an ice chest on wheels to make it more portable. for less than $200 total, something like that should last a long time. i would put the battery on a trickle charger to keep it fresh and ready to go.

forgot to mention that i had tried using his car battery charger/jump starter, too. it wouldn't work at all for me.