A type 7 U-boat had 2 battery compartments called " accumulator room 1 and 2 ( #1 was aft and #2 was forward ) . There was an access hatch to each. This battery room or compartment was so tight for space that above the batteries was a set of rails with a small trolly for a man to lay on and slide over the tops of the batteriers to check them or to make repairs. The batteries were of the rubber lined ,lead -acid type. The forward room had 62 cells in 9 banks and the aft compartment also had 9 banks but 1 extra cell. Each battery compartment could supply about 11,000 amp/hrs of power. Each boat carried several spools of heavy cooper wire and wire cutters to jump a cracked or damaged cell. If a man went down into a battery room he may bring his Draeger rebreather apperatus just in case of deadly gas buildup. He also would bring some litmus paper to test the batteries for saltwater contamination.The electric motors used were made by BBC,SIEMENS OR AEG at full underwater speed of 7.4 knots these motors draw 720 amps .