When I saw that the T-3 had such a small battery, I thought RIDICULOUS! A base should have 24 hr Battery life!! So, my thoughts are: Just PLAN for an auxiliary external battery. UNLESS it is just for a short time use, like a couple of hrs work, close to the base.
And, why would Javad and company make it with such a small battery? I don't know. But, I'd guess it's due to future plans, to use it as a rover, or NOT transmitting, or they were cobbling parts, and this was somehow easier. Fact is, I do not know. But, if you plan to use a T3 like a T2, with it's internal radio, get you a nice big 55 AH SLA battery, and a good charger, and "Let 'er rip, tader chip!"
Nate