One central bolt withdraws 3 locking arms that secure the hatch, which is sealed with a substantial O-ring. All batteries, both port and starboard, are serviced through this one hatch. I know it's fuzzy, but it's the best I could do. Here is the interior, which is very aerospace-like in construction. Some details of the fine riveting and lightening holes in the structure may be seen.
Structural strength is immense.
Peering into the battery hatch, we can see the battery trays, cables, and more of the method of construction. Batteries slide into the brackets shown and are fully secured both top and bottom. Here is one of the batteries, sitting and ready to be installed. Some of the DPV's have been retrofitted with sealed lead-acid batteries by guys who could not get the originals. In typically Russian fashion, the DPV was provided with sufficient spare parts to be maintained for the life of the unit.