Batteries topside or in wtc?

hi everyone

I am relatively new to the rov building game and I was wondering what sort of solutions builders had come up with for the following issues with batteries:

1/.topside or attached to rov or inside or wtc. (when I say topside, I am assuming the new tether will carry power down)

2/if in the acrylic wtc or other custom watertight container, what sort of saltwater resistant external connectors could you use so you don’t have to take the batteries out to recharge them at the end of use?

3/. what sort of batteries, how many and what ah should I be looking at?

hopefully somebody has the time to reply and save me blundering further along with my low knowledge base and stop me adding to my collection of wrong direction prototypes cluttering up an already cluttered workshop.



Hi John,

Thanks for the post. These are good questions.

  1. Our stuff is designed to be battery powered with the batteries contained on the ROV. It’s pretty difficult to send power down through the tether due to power losses in the long tether. On commercial ROVs this is done with high voltage (300+V) power.

  2. There are connectors you can use but most are fairly expensive. You can look into Subconn and Seacon. There are some available on Make sure they have enough current rating to handle the thrusters. You may have to double up pins to get that (like 4 pins positive, 4 pins negative, for example).

  3. I would recommend lithium polymer or lithium ion batteries. We have a battery guide on our documentation with some recommendations: Battery Selection

I hope this helps!


Although from a technical point of view Lithium batteries are by far preferred ( highest power density, low internal resistance, no memory) there might be a different kind of problem: IATA is very strict on air transport of (high power) Lithium batteries. As far as I know, they are banned from passenger aircrafts and even on cargo aircraft strict rules apply. See IATA - DG Documentation and IATA - DG Documentation

Does anybody else on the forum may provide with additional information on this subject?


Here is what has to say about shipping Lithium batteries:

To follow US DOT and IATA shipping regulations, there are limits to the quantities and capacities of batteries that can be shipped via air or ground, with additional limitations on air shipments. Below are the current shipping rules/restrictions for batteries ordered from RMRC. If an order is received that violates the restrictions, RMRC will cancel the order or remove some or all of the batteries from the order and ship the remainder of the order at our discretion. A refund will be issued for any items removed or canceled.

GROUND SHIPPING (FedEX Ground (Canada & Mexico as well), FedEx Home Delivery, UPS Ground, USPS First Class, UPS Standard):

  • The sum of all batteries cannot exceed 3000Wh.
NO AIR SHIPPING (International Air, FedEx 2 Day, FedEx Overnight, UPS 3 Day Select, UPS 2nd Day Air, UPS Next Day Air, USPS Priority Mail, USPS Express Mail)
  • At this time, because of the 30% state of charge rule for air shipments, we are unable to ship batteries to customers using any form of air shipping. Sitting for long periods at a 30% state of charge will reduce the battery performance, which is unacceptable for us and our customers.
Shipment of Lithium batteries is based on the total Watt-hr (power) of the battery or batteries in question.




Hi guys,

I am also trying to building an AUV, similar to standard BR ROV but on different frame. I will use 6 T200 thrusters and 4" WTC. I have got a few technical questions:

  1. What is a max weight of the rov. looks like my will weight about 10-12kg. Is it not too much for this thrusers?
  2. Length of the tether. Have anyone tested BR ROV with about 100m tether with stronger current? (2-3 knots)
Many thanks for a help.



10-12 kg is just fine as long as the vehicle is still close to neutral buoyancy. We’ve used the T200s on ROVs up to about 10kg and they are much too powerful most of the time. Some people have made much heavier ROVs with them.

We’ve tested in currents of about 2 knots (1 m/s) and the ROV can handle it fine but battery life is significantly reduced, of course.



@Rusty-How in the world do you fit enough battery, let alone the electronics, in a 4" x 12" WTE to handle 6 T200’s in full stabilization, 3-axis, mode control (as in a AUV)? I would think if there was any current or wave action, or buoyancy vs CofG imbalance, to speak of, there would be a large, continuous current draw.


Thanks Rusty,

I was worrying about dragging the cable by the current. 100m, is a quite long cable.

Also, I have noticed there is a lot of forum users trying to power up the ROV by the tether. I know your recommendation is to use a battery pack on the rov but have you thought about something like Ethernet over DC Power line(EoP)?


@Richard - You are right. You’ll burn through your batteries pretty fast in a current. We are working on some ways to fit a lot more battery power onboard and that makes a big difference.

@Tom - There will be quite a bit of drag on the cable but the BlueROV has quite a bit of thrust to resist it. If you want to maximize runtime at depth in strong currents, I would recommend adding a weight on the tether so that it hands straight down from the boat and the ROV only has to drag a small portion of it in high currents.

As far as power over tether goes, we’re aiming towards the Ethernet over DC power line approach eventually. While this is relatively simple to get set up, we want to make sure it is 100% safe since there will be high voltages involved.