Sharing some battery tech I'm developing

Here is my first and newer verson of a long duration high safety battery. Both these batteries are being developed with used Sanyo 18650 GA cells, but the end goal is to make the larger 21P packs with Samsung INR 18650 30Q or Murata INR 18650 vtc6 cells. The smaller one has a max output of 80 amps which is fine for 6 T-100s, currently used on our ROV. But moving on to T-200s we will need to limit motor current or get better cells.

This battery utilizes a 6s or 4s 21p arrangement with 3 different cell selections.

Cell selection:

Murata INR 18650 VTC6 3000-mah
15-amp continuous
30-amp peak
Nominal 3.7v
Assembled pack: 63-AH
Assembled pack: 315-amps continuous
Assembled pack: 630-amp peak
Nominal 22.2volts
Use case: 8xT-500 thrusters

Samsung INR 18650 30q 3000-mah
15-amp continuous
20-amp peak (100% charge state)
Nominal 3.7v
Assembled pack: 63-AH
Assembled pack: 315-amps continuous
Assembled pack: 420-amp peak
Nominal 22.2volts
Use case: 6xT-500 thrusters

Sanyo NCR 18650GA 3500-mah
10-amp continuous
Nominal 3.7v
Assembled pack: 73.5-AH
210-amps continuous
Use case: 2xT-500 thrusters and 4xT-200.

I wanted to share my designs so you all can see. The smaller diameter battery, for 3 inch by 14-inch canisters, has a 100-amp BMS and a 60-amp fuse, which is significantly underpowered for the ROV2 but works without issue on our robot.

The battery also utilized 3D printed dividers that can make the battery safer for long term use. Damage to cell wrappers or lack of air flow can be detrimental to cell temperature or cell life.

Eventually I want to develop my own BMS that can be specially sized for the larger 4-inch canister 21p battery. We are also using recycles cells, which I do not recommend, but we have a bike shop in town that gives our robotics team their old bike batteries.

Thanks for taking a look! at the current moment I’m mostly just developing this for personal use.


Nice design! I have built a few packs with 3D printed spacers a lot like yours.

After some close calls with LiPo’s I switched mostly to LiFePo4’s, or 18650’s.

Here are pics of the units I put in series (18650, 26650 LiFePo4, and a 32700 LiFePo4 on the bottom):

Cool! I have built a pack with 18650s and one with 21700s. The 21700s are just a little too long to fit inside a 14inch canister. And with 50e cells the power output is a littleack luster. 4s 7p Samsung 21700 5000mah 10amp cells.

Now if I could get myself some vtc6a 21700s with 4500mah and 40amp output that would be really cool.

One of my design chooses I’m not so sure about though. Instead of connecting the battery segments together I’m using 6 m3 rods that since all the nickel strips together. And I cut releases for the balance leads. There doesn’t seem to be any current carrying or voltage drop issues but I’m not sure about longevity especially with corrosive salt water. I’m using all stainless steel threaded rods.

Another part of my goals is to be renewable. All the cells I’m using are used cells from. Bosche bicycle batteries that were donated from a local bike shop. A lot of these cells are what would be considered not good examples. A lot of them Auto discharge slowly because they were discharged down to .33 volts but all of them test within 85%+ of their capacity and most test about 95% of their capacity. That’s really good for 3-5 year old cells. I have one or two sales testing at 3450mah and on The low end some are testing at 3100mah. These are mostly sanyo inr 18650 GA cells rated at 10amps 3500mah.

I have had some worst cells rated at 2900mah but only tested 2100mah. These ones were also not over discharged much. Those ones are going straight in the bin! For future projects.

This is my testing setup, I have a charger that I just used to bring cells back up to fully charged. Then I test all of them with a litokala tester.

I love batteries!

Also saw that you make videos and wanted to share a few we have made with our ROV.

This is a cut down video of our project removing sea debris. We managed to get a license for ocean cleanup earlier this summer and removed some derelict fishing gear. I am a member of the Port Townsend STEM club and mainly do ROV electronics.

I only charge the batteries to 16.4 volts usually out of 16.8 and during this whole day, roughly 4-6 hours, we only droped to 14.5volts. that’s roughly 50~60% percent used. With used cells!

Hi @BatGuy, welcome to the forum! :slight_smile:

Thanks for sharing this (and @nperry for sharing yours too) - lots of interesting information in this thread, including some helpful tips for others who are curious about safe battery pack designs and cell considerations.

A reminder to anyone looking to try these things themselves, lithium-based batteries can hold a significant amount of energy, and are dangerous if not handled properly. Proper separation, electrical insulation, and cell balancing are very important, along with avoiding current draw beyond what the cells are rated to provide. Temperature and current limits are worth putting in place (via sensors and software or components like fuses), and cooling can be worth thinking about.

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