How many amps a battery can put out is generally expressed in it's C rating, that is amps=C rating*mah so for example, a 40C*3000mah pack should be able to produce a constant 120 amps. Double check the ratings on the packs you're looking at, even for the low mah ratings common to 1/18th car packs, that seems to very lowly rated. Also, check the burst rate. It's usually double the constant rate, whereas a motor is usually rated at it's max amp draw. A motor that is said to draw 41 amps will do so only under max load but a 45amp pack should be able to burst to 90amps - more than enough of a gap to work Ok.