Linking 2 batteries

Currently i have 2 batteries mounted on my SP140 trike.
One as per original design and one under the seat
I have joined them together with 2 cables 7G which are both 0.5 metres long. The ends of these cables are soldered together and join a short cable with original connector. This plugs into the controller.
Each battery also had an original connector in place. So total of 3 connectors in use.

When i connect the batteries, i do so by first touching the connectors together on the top battery, waiting for the audible response and then fully inserting the connector together. On the bottom battery i do not pause during connection
This method seems to work well the majority of the time.
One time however, during flight i realised that only 1 battery was discharging. I believe this may have been caused by pausing during connection on BOTH batteries. That assumption is only a guess.
And then yesterday during flight, i again noticed that only one battery was discharging which made me decide to return to the landing zone.
This may or may not have been caused in a long delay at the launch site where the batteries were connected but not “armed” for close to 30 minutes.
Upon decent into landing with motor not in use for close to a minute, the batteries decided to both come online together and the display showed battery level had gone up to 97%. So i continued flying for another 30 minutes without further problems
I would like to hear from anyone who can suggest a better way to connect the 2 batteries to make flying safer and more reliable

Hi Tim. Sounds like a nice flying machine, hope you will post pics or video!

It sounds like the BMS on the second battery does not “wake up” because it’s not detecting current flow when you connect it (this is logical if both batteries are charged and have almost the same voltage).

One easy thing you could do is add a “start” button to the BMSs, from the manual it looks like this is possible, see below J5 “trig” connections.

Another way would be to leave the BMS out of the picture for discharging, and connect the ESC directly to the pack terminals - with the equal length cables as you said, and a fuse each. However to do that safely, you (or the controller) still has to take the cell conditions into account - cell voltage and temperature.

On this thread you can see the preparatory work for that, but it doesn’t exist yet and will need some additional wiring to make it work. It’s even trickier for two packs so maybe don’t hold your breath for this!

Try to connect two batteries in parallel first and first after that connect them to ESC. This way the current will flow through both of the batteries at the same time during ESC activation, thus hopefully triggering both BMS.

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Hi Evan,
thanks for your feedback. I have shared many photos and videos on the SP140 Facebook page
I will share what you have suggested with my brother who is a lot more tech savy than i and a what we can come up with
Thanks again

Yes this a good suggestion thanks
I will need to order a new plug as one was damaged when it overheated due to faulty soldering