Romulus uses two sets of NiMH Batteries. The batteries are capable of 24V and 4500 mAh. The batteries are interchangeable. When the vehicle is in operation one is attached to the thrusters and another is used to supply the computer and the sensors. The reason that we have the batteries completely separate is to reduce electrical noise to the more sensitive portions of the AUV.
They are located at the far left of the computer housing case. It is apparent how easily they stack on top of each other. While they are relatively large and heavy, they work perfectly with the rest of the system. They are held together by strips of Velcro, which has a spotless record of keeping them in place.
One of the recent changes to the batteries, and the way the vehicle is powered, is the use of the pair of NiMH batteries. In years past the computer and sensors were powered by a Li Ion battery. This was lighter and gave plenty of power. This year there have been a number of new Navy safety regulations enacted dealing with Li Ion batteries and power supplies.
The team decided to move away from these as a power source to avoid the hassle and time drain that going through the new procedures would have entailed. The second NiMH may be heavier than the Li Ion battery was, but it greatly simplifies dealing with the batteries overall. Having interchangeable batteries is an overall improvement for the vehicle.
The team will travel to the competition with 4 NiMH batteries. This allows us to keep two charged, or recharging after a test run, while two are in the vehicle, as we are testing it again. When we are working out of the pool we can hook the vehicle to 'shore power. The lifetime of each battery is more than sufficient to keep the vehicle operational whenever we want it.