greetings dacostasr as sownare has said the pershing lower hull is a very tight fit even if you go by instructions for arrangement of components and battery placement so battery size is very important i do not know exactly what my battery size is in mah but the measurement is 1"x 1 7/8"x5 1/8" i'am guessing at maybe 3800? i have run the pershing for about 50 min. and not run battery completely down so this is food for thought or maybe if you know somebody that has different size batteries and try them to see what fits the bestdan