JB3 draws ~250 mA. V3 draws 600-1000 mA (depending on mics and ADC settings), IME darn close to 1000 mA using my Schoeps with the ADC on. UA5 draws ~450 mA. So...
JB3 + UA5 = 700 mA
JB3 + V3 = 1250 mA
Most battery ratings, for example a Li-Ion DVD batt at 5400 mAH, are based on a sloooow discharge. But our power-hungry devices discharge the batteries very quickly, relatively speaking. In general, the faster the draw the worse the relative run-time, i.e. the less efficient the use of the battery. For example, let's take device A (500 mA draw) and device B (1,000 mA draw). Device B draws double the juice as device A, we might expect it to achieve 1/2 the run-time using the same battery. However, due to less efficient use of the battery at such a fast discharge rate, device B will achieve less than 1/2 the run-time as device A.
I'd expect far less run-time out of the JB3/UA5 combo as the JB3/V3 combo given the significantly higher draw. But then again...maybe the Li-Ion indicator lights are very conservative in their configuration and you had more run-time left than you thought? Did you have a full charge?
Best bet: double check all your cables for shorts and run some tests at home to simulate field usage and see what happens. That's the ONLY way to know for sure what sort of run-times you'll achieve with that setup.