just wanna add not any accu can provide high discharge rate so be careful when choosing accu.
discharge rate mrkes in Cs - Coulons ( i don't know is it correct write in english) so for example in this threadviewtopic.php?f=26&t=6097
you can see on images of accus numbers like 20C 26C or other it means that accu can provide 20xcapacity discharge power, so if you have 3000 mAh accu which have 20C discharge rate you can draw 60 Amps from it.
discarge rates which near critical for particular accu will shorten accu life. so if you use yours at max discharge rate it may shorten charge cycles from nominal 1000 to 100 for example.
shortly speaking if you planning around 20A draw and accu around 3000 mAh discharge rate should be at least 10C but better to have 15 and more.
try to find something related to RC models, these accus usually have high discharge rates