Questions on Vex V5 Part Reliability

What is up with the stupid V5 parts breaking all over the place? It’s so easy to accidentally break a V5 brain port, (like 3 of our brains) and just by sitting around for the summer, 2/3 of our motors locked up! Also, our batteries are going on the fritz left and right! They keep flashing a dull red, and won’t give charge, even if they are charged. Anyone else having this issue? Good ol’ V4 was hecka reliable. Not V5.


Actually, anyone have any info on those batteries going on the fritz?


Our experience has been the opposite. v4 batteries & motors ate up majority of our budget because they never seemed to last. v4 batteries & motors had constant broken wires.

We haven’t purchased a single motor or battery this year, relying on last year’s purchases. Our experience is that v5 has been extremely reliable, allowing us to use our fundraising more strategically.


Well, I mean reliable in the sense that if they break, they are: A: easy to replace, or: B: easy to fix.
We got V5 a year ago and we were awestruck. Now we are frustrated with this issue of the parts breaking.

V5 batteries are lithium ion
You have to store them like computer batteries which if I remember is 60% charge for long periods of not using

The V5 battery chemistry is lithium-iron-phosphate, or LiFePO₄, not lithium-ion.


The Cortex and V5 systems each have their own fair share of issues.

With most of the Cortex parts, mechanical damage (shorting wires) was the greatest problem. If Cortex parts are treated with care, they can last for many years without any major issues.

With V5, electrical issues seem to be the greatest problem; V5 is generally quite a bit more mechanically robust than Cortex. In theory, if treated with a similar level of care, V5 parts should also be able to last for many years. However, due to the nature of the recurring V5 issues the community has seen, it is still not sufficiently clear what exact practices are most effective in mitigating V5 issues.


For my team we ordered 2 V5 kits for two teams in march and we haven’t had any problems yet as of now so I would like to hear more about how your problems occurred

The best advice I got with regards to V5 is to get a cable tester to check smart cables. New stock and custom cables should be checked prior to connecting to V5 brain. This may help with some of the burnout ports. End of season check all cables before putting them back into circulation.

Batteries, leaving them in chargers and discharging guidelines should be followed. Do not use the ret button as a “fix” but follow the guidance for battery management and diagnostics on

Motors - if it seizes, contact VEX Support to see if they can replace them.


Can you recommend one?

Robosource has one available:


I ordered a couple of those testers, watched the video on how to use the tester but it isn’t ideal for our students.

"You'll notice that the connector is a six pin connector, however 
vex v5 cables are only four pins ...   you need to be careful of, is
while inserting the cable, ensure that it is centered in the connector"

Our kids had a hard time being sure it was centered. So if it didn’t pass, they didn’t know if it was the cable or their placement of the connector in the connector.


It is centered when lights 2 - 3 - 4 - 5 light up. However, I do wish the 4-wire cable snapped into place. I taught a HS team member how to use it. Although, I could see that it may be difficult for a middle schooler to use.


May be fixable, though, it would be cool if there was a 3D printed insert that would ‘guide’ the connector to be centered.

That’s our challenge, we’re a Middle School program with 6th through 8th grade students.

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THAT would be super cool. And totally do-able.


Not sure if you’re on the FB VEX Coach’s page - but I posted a challenge to the coaches for someone to come up with something like this.
(editted - because, well, English)


It really seems like someone with the know how, ought to be able to wire a 6-wire end male plug onto a 4wire extension or splitter, such that the wires would be connected in the right way.

It sounds like a pain in the butt, but maybe robosource can be convinced to start making something?


Our only issue has been 1 bad battery, and one team has killed a platoon of motors, so I’m blaming them/ their code, but we have had issues with ports breaking, luckily you can only use 8 of the 21

It would be easy to build an adapter but I was able to find one on eBay.


Is that something the vendor makes? I would worry that device might introduce even more uncertainty. If a wire fails, what failed, the two of these adapters (you need two - one for each end), or the actual wire?

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