V5 battery design question/suggestion

I had heard that it was possible to disassemble a bad V5 battery and swap out individual bad 18650 cells with good cells from other bad batteries, but the way the batteries are connected (at least in the one I’m looking at) seems to make it pretty much impossible to reassemble the unit after swapping out a cell.

I’m wondering why it wouldn’t be possible to drop the hardwired (?) cell-to-cell and cell-to-PCB connections and instead have snap-in cells like in a normal consumer appliance. And also an easy-open case. Such a design would mitigate what I regard as the unacceptably high cost and failure rate of the current design.

It’s just a different design paradigm used for applications where they have no trust for the average customer (15 year old children). So they intentionally seal the battery and don’t want anyone to open it. Now hopefully this philosophy is paired with really reliable hardware.

Swapping cells would also make the battery not completion legal, screwing with battery wrong could result in breaking your v5 brain as well as the battery itself.

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Thanks Griffin for your thoughts. I could live with the kind of design thinking you describe if as you said the battery hardware was really reliable. Which in my experience it isn’t. Given that, I don’t think the idea of a new battery design involving replaceable cells is unreasonable, nor would it be outside the capabilities of a typical VEX student. I realize that this would require a minor rule change but that seems like not a big deal.

Hi David, you might want to reach out to VEX support and talk to them about your battery issue. The packs do come with a warranty and you may be able to get them replaced.

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Thanks Foster, I’ll plan to contact them. I’m new to the forum, but I brought the subject up here because I was thinking that perhaps VEX monitors it and would respond – that way others could benefit from the response as well.

BTW unfortunately all our batteries are out of warranty. But in general I’ve not been satisfied with their service life given how expensive they are and how rugged they appear to be.

Vex support is always best F2F. We can help with some things but calling them should always be first. Good luck

Staff from VEX do monitor the forums.

can you give some examples of the issues you have had.

One big issue if cells were user replaceable is that of competitive advantage. Past experience from the cortex system which used essentially standard 7.2V NiMH was that teams would try and over volt (ie. over charge) batteries, the GDC had to get very strict on only allowing VEX chargers to be used. If the LiFePO4 cells were user replaceable it would be hard to stop higher capacity cells being installed along with other possible illegal modifications.

There are also safety concerns, individual cell voltage has to be monitored along with pack temperature, this is simplified when the end user does not have access to the internals of the pack.

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Additionally… large current and spring terminals don’t mix well. Then there’s another issue of cell selection when replacing cells, loose cells ending up on the floor, etc. If your batteries are failing early… something’s up.

I’m not sure it’s because of the age of some of the batteries we have, but two of ours no longer power the robot and show a red blinking light at around 50% capacity.


It’s like this but sometimes it can do it at 2 or even three lights showing.

I’m not sure what to do, these batteries do this every time we try and use them, we’ve just set them aside because we don’t want it to happen in competition.

If there is something I’m missing, I would like to know, thanks

Thank you, those are really helpful insights.

Ok, thank you, good point.