Ask the experts, trident is completely sealed inside it?


trident appearance is very beautiful, very different with the 2.8, I do not know which is also used cylinder seal it? So many traces how to deal with?


Replacing the battery on Trident


Sealing method for the Trident is still being determined, we have a couple options we are testing right now. Once more details about Trident are finalized there will be a more official announcement and we will likely have answers to questions like this about Trident.

2.8 uses an o-ring seal on an acrylic cylinder.


OpenROV Support



I have read on the forum that in order to improve reliability, the batteries and other electronics are mounted permanently inside the vehicle.
Does that mean that we are not able to change the batteries or other electronic components ?
If your answer is yes, what happens at the end of the batteri life ?
Sending it back to Openrow just tonreplace the batteries would be a verry expensive operation !



I never got an answer to this question !

In my opinion it is important to know if the batteries can be replaced by the owner or not !


Hey Marcolinger - sorry for the delay in reply! You are correct that the batteries and electronics in the ROV will be factory sealed in order to maintain robustness. Issues with hatches and sealing surfaces are one of the main failure modes in underwater vehicals and we didn’t want to add any undue risk there. That being said, we’re using high quality, name brand, Lithium Manganese Nickel 18650 batteries that are optimized for cycle life and are attached to a specially engineered charge management system. This system will make sure the batteries are kept in good health and I don’t expect that you’ll notice any significant degradation in battery performance over the lifetime of the vehicle. Especially because of our heritage with the 2-series kits, we really wanted to make Trident as hackable as possible, but in this case making the vehicle extremely reliable in the field was our main priority. I hope that answers your question! Eric


Thanks for your answer !
Are you sure that this is a good solution ? I doubt. I can understand a complete sealing for a tool which is used more or less each day (toothbrush, professional driller, …) but in a ROW number of people will use only during holidays or longer week-ends, the batteries will not last years if not discharged and charged on a regular basis.
What happens if a engine breaks ?
Will your customers be happy to invest more then 1.000 $ knowing that ther Row is worthless if they forget to charge the battery or if an engine breaks ?


Hey Marc,

I see where you’re coming from. Happily, the motors are replaceable if they get damaged. We’ve been designing the propulsion system to be as robust as possible, but for moving parts, it’s always a good idea to have maintenance capabilities. Since the batteries are static and the main thing that could ruin them (and the vehicle) was flooding, that was the part we decided to put inside the sealed portion of the vehicle. The batteries also have electronics wired to each individual cell in the packs for balance discharging, so a user pluggable system would have added a lot of cost and complexity.



Hey Eric,

Thanks for your answer. I appreciate.
I have read that these type of batteries have a lifetime expectation from 3 to 7 years. Is this correct ?




Hey Marc,

It’s hard to say exactly. We’re using very similar batteries to what are being used in the Tesla Model S. In fact, the price of the battery has been affected by Tesla buying them all up! By the way, what are you planning to use the ROV for?



Interesting topic, I searched around a bit and came up with the following info:

Lithium Nickel Manganese Cobalt Oxide batteris (LiNiMnCoO2 / NMC) are quite modern. For example, the battery pack in the Nissan Leaf was just upgraded to NMC cells this year. The Tesla Powerwall and the Zero electric motorcycles also use NMC cells.

The Tesla Model S and X apparently use Nickel Cobalt Aluminum Oxide (NCA) 18650 cells.

So far I haven’t found any evidence for charging and discharging Li-Ion batteries on a regular basis to “maintain” them, this would actually only degrade them further.

After 1000-2000 full charge/discharge cycles, NMC batteries should [retain 80%] ( of their original capacity (2nd source). This assumes a full discharge of the battery per cycle – if it’s not fully discharged each time, you could have a few thousand cycles more. This also assumes the battery is charged to max 4.2V/cell.

Also add to that a percentage of irreversible capacity loss per year: Table 2 on states that Li-Cobalt based batteries permanently lose 4% capacity per year if stored at 25ºC and 40% state of charge, while storing it fully charged leads to a 20% irreversible capacity loss per year. NMC cells might be slightly different, but I’ll use these numbers for the calculation below since I haven’t found anything better.

According to an abstract here, an NMC cell stored at an empty state of charge (~3.0V) showed almost no change after a year.

It seems the prudent thing to do is to keep the Trident in a cool place and discharge it to 40% SOC (~3.7V) or lower for storage (if discharged too low, it’s possible the cell could drop below 3.0V during long term storage and be permanently damaged).

So, let’s find out the run time after 4 years of high use:
The Trident has a listed 3 hour run time. Let’s assume it’s used on average twice per week (104 times/year), each time fully discharging it during use and storing it at 40% charge at room temperature. Interpolating in a linear fashion, after 4 years (416 cycles), this would cause an 8% irreversible capacity loss, add to that 16% loss from degradation over time = 76% capacity = 137 mins theoretical run time after 4 years.


Hey Eric,

I am retired, live most of the time in Luxembourg (no interesting place for the ROW) and several months in the year in Sardegna (Italy) at the border of the sea. Having since ever played with RC planes, cars and ships and drones, my children offered me the Trident. All this to explain that I will use it only periodicaly here in Sardegna. This means that I hope to use it over years but not each month.

As a lawyer I wonder if you are not taking a serious risk to sell a product knowing that there is included a clearly limited lifetime piece and not giving the possibility to replace that piece or, at least, indicating clearly beforehand that this limit exists. Under most european legislations I think you risk to have problems.

Giving the possibility to open the ROW and giving clear instructions how this has to be done, that rings have to be replaced by original ones a.s.o. gives you a lot more comfort from a legal point. See all the action cams (I jave a Sony and a GoPro) where this is standard.

Greetings from Sardegna,




Thnka a lot for this interesting contribution !

The example you take is one of a professional user. Progressively charging and discharging will reduce the charge capacity.

What are your conclusions for a “holliday user”, someone who uses it only on vacation several short periods a year. The impact of charging and discharging will, I suppose, be the same. But how long can the battery live ? After how many years will she be dead even (or because) she was not used regularely ?




Hi Marc,

Yes, I was going for a worst case usage scenario. As a holiday user you actually should be even less concerned about the battery. I’ll assume you’ll fully discharge it <20 times per year, in which case you can expect a negligible theoretical degradation (caused by usage) of 2% after 4 years.

In this case the storage conditions would be the determining factor in capacity loss, so assuming you store it at <40% state of charge at <25ºC, the battery should have at least 80% of the original capacity after 5 years. This is plenty, so I’m not worried about that.

It’s more likely that the electronics fail or that I lose/damage it before the battery dies.

I don’t mind the non-replaceable battery, these are not unusual and quite commonplace now. For example the popular iPhone, iPad and MacBooks, non of which have user replaceable batteries but have much higher cycling and are expected to hold up for many years.

As mentioned this battery type is also used in the world’s most popular electric car (Nissan Leaf), which is a US$30.000 product that owners are expecting to last for years, and where the battery is also not user-replaceable and degrades similarly to the Trident, so that’s definitely not a new/big issue.

It’s safe to say that modern battery chemistries (especially NMCs) are much improved compared to their older counterparts.

I’m actually quite happy that in return the unit is sealed, as I know from experience (unfortunately) that a watertight O-ring that has to be regularly checked, cleaned, maybe lubed and put back into place (sometimes on a boat in rough seas, sometimes in the rain, sometimes in a sandy environment which is really a pain) is a common point of failure and for me a larger concern than the battery, therefore I actually think it’s quite great that this failure mode is eliminated so that I don’t have to worry about a good seal anymore!

Especially as a holiday user this should make the device a lot more appealing - plug and play.

@Eric_Stackpole Are the assumptions I’m making here correct?


Again, thanks a lot for your contribution !

I am far more optimistic now !



@keenmetal and @marcolinger - I’ve enjoyed this discussion! @keenmetal - your thinking is very similar to ours was when deciding to factory seal the batteries inside. We just didn’t want to take the risk from added complexity and failure modes once it’s away from the production line. @marcolinger - you’re also correct that we should describe what people should expect about cycle life, etc, but we don’t want to speculate on that before we’ve properly examined the performance of the entire system over time. Our Kickstarter supporters and pre-order customers are paving the way for this technology by getting Trident before it has been extensively characterized. We understand that being an early adopter assumes some faith. We’ll do our best to communicate clearly about performance expectations once we feel confident about them, but for now it would be very speculative to give any specific numbers.

Thanks again for the comments!



Thanks for your openess and clear answers ! I confirm that I have full confidence in your team and will cerainly be happy with the Trident you will deliver.

To complete what Keenmetal wrote, apple portable products are sealed but apple offers through its apple shops and autorized sellers the possibility to have the batterie changed or to have a eplacement product. Perhaps it would be good, once the product is mature to give not only the life expectation pf the batteries but also a possibility to send the product to Openrow to get it repared, even if the price of this sending and repairing might discourage people of doing so.

All the best



Hi @Eric_Stackpole
Just following on from @keenmetal excellent work re the Lithium Nickel Manganese Cobalt Oxide batteries (LiNiMnCoO2 / NMC). Not knowing exactly how you intent to charge the Trident I am just assuming the aim is to just disconnect the 2 twisted wire neutrally buoyant tether and plug in a power supply instead of the tether (I am assuming this is the case and the Trident basically has an inbuilt charger)

This gave me a thought. How smart is the charger?

Given Mark’s observations RE charging is the charger (if in built?) capable of having a couple of different charging patterns i.e.

  1. A rapid charge (ie charge up the batteries as fast as possible even if at the sake of a few future life cycles) just to get the unit back in the water for expeditions away with time constraints

  2. A standard charge say 1C (C-rate) for the general purpose charge

  3. A charge or discharge cycle for longer term storage or the ROV to Marks “40% state of charge”



Hey Scott,

Sorry- I missed your reply earlier! You’re right about charging method. To charge Trident, a charger with a tether connector on one end gets plugged into where the tether goes on the vehicle. We’re planning to charge the vehicle at a rate of about 0.25C which is about the right intersection of reasonable speed (takes about 4 hours to charge), battery longevity (the rate is low enough to keep the batteries in good health long-term) and temperature (the rate is also low enough to keep the system from heating up too much during the charging process). With this charging rate, we don’t think there will be an extreme need to add different charging modes and we prefer to keep the system relatively simple.

Thanks for the reply!