SLA batteries have rubber caps that play the role of valves for the release of gases when the battery is charged. These caps are tightly pressed with plastic caps and do not allow water to pass even when immersed in great depth.
We used XT60 connectors underwater with a small amount of a thick grease on contacts. It is inexpensive and works perfectly even in sea water. Similar connectors have been working on our ROV for two years and still do not require replacement.
In water two DT700 motors can consume a current of 50 amperes maximum and develop a maximum thrust of more than 7,5 kilograms. This is a very good result, but in order to increase the battery run time, we have limited the current to 30 amperes maximum. To do this, just limit the movement of the slide resistor. We knew it theoreticaly and tested in practice, that at higher current the speed increases insignificantly, but the operating time is greatly reduced. With this current you can swim continuously with a maximum speed of 1.85 mph (3 km per hour) for 8 minutes with one battery or 20 minutes with two batteries.
Battery 9 Ah weighs 2.5 kg on
the surface, but in water 1.5 kg only. Usually we use two batteries
at once connected in parallel. One on back and one on stomach.
Batteries are secured to the strap using velcro. This is very
reliable and allows you to quickly replace the batteries with new