To be brutal, sorry, Amp/Hours is Amp Hours. Period. If you want extended use at high current, you're going to need high Amp/Hours. Battery packs from portable equipment are not THAT good in 100% duty cycle under load. You might consider sealed lead-acid from a HAM radio supplier or Gel-Cells from alarm / emerg lighting systems. Both are rated for 100% duty cycle. Both are availabel in moderate sized (weight) packages. Wet cells are highly recomended AGAINST for portable use. The bottom line comes back to the load, Amp/Hours... (It's like Lazarus Long says; There ain't no free lunch)