Recommendation -- portable battery jumper

[Lawrence Bardfeld]

[Yes, I really did make a good faith attempt to search the archives first.]

Can anyone recommend a portable battery jumper/booster (or whatever they're 
called) -- or at least tell me what I should look for (e.g., peak amps, or 
specific manufacturers to avoid)?  Yesterday I unsuccessfully tried to 
restart my car using a low-powered Coleman unit that was supposedly fully 
charged, and it didn't work.  (I suppose the connection could have been the 
problem, but am pretty sure it was secure, so in disgust I'm looking for a 
better unit.)  Fortunately at the time I was parked outside my local 
recommended Audi mechanic (Woodlawn), having accompanied the tow truck that 
brought my S4 there, so I was easily able to get some assistance.

Thanks,
Larry
'93 S4, etc.