So this is our team’s first (and as I say only) year in Vex, I was wondering when we go to competition events how many batteries do you guys bring with you? (regional or local). I was planning to bring 1 but I feel like that would run out of charge before the end of the tournament ( and I have no idea if charging batteries is allowed either).
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I would recommend bringing at least 3 or 4. You are definitely able to charge your batteries between matches, but I recommend having a new battery with complete charge for each match. Then you can continue using that battery between matches at practice fields or just for testing. Although vex claims that the robot performs the same regardless of battery percentage, my experience in testing has shown otherwise, so I ALWAYS recommend using a fresh battery for matches and skills.
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I agree with the poster above. My team would usually use between 3-6 batteries for 6-8 matches and 6 skills runs.
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Not quite true… VEX testing is pretty extensive with batteries using same charging practices (meaning do not leave in charger over long periods of time - say Covid lockdown which prevented us from disconnecting batteries from chargers for many months…)
There are good tools built into V5 Firmware Utility (battery medic) and information articles in library.vex.com that will help bring best practices for battery maintenance, storage, and competition operation.
If you have specific testing data to share, vs anecdotal experiences - please do … best to shine light on how to get best out of batteries …
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This past year, I did extensive testing with the accelerometer and as the battery percentage lowered, the acceleration and maximum velocity of the drivetrain decreased. We did testing on this for about 10 hours this past semester taking into account 2 major factors, the battery percentage and temperature of the motors and while the motor temperature has a larger impact, the battery percentage was also a factor.
I did not take into account factors such as how old the battery was or look at their diagnostic information, or which batteries were overcharged etc as these were not factors that could easily be controlled or measured.
So it might be that batteries that are perfectly cared for and never get overcharged and never have any issues with them provide consistent power at different battery percentages. From the real world testing on a robot, the battery percentage does have an effect on the robot performance.
While you are welcome to request anecdotal or hard data, I do not appreciate your response to my statement “not quite true.” I find it quite rude when I have in fact done extensive testing on this exact subject.
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Take a step back - VEX has been very clear about their assumptions, responding to concerns about battery health, and providing ways for teams to examine their assumptions with apps to support detecting of health/failures (Battery Medic… )
Look forward to you publishing your test procedures and results. That is engineering.
What you describe as factors of poor performance, motor temperatures (indicator of friction yielding inefficient performance not accounting for design of subsystems - like motors)… eg. how you use the motors may impact how your battery may last is not an indicator of how the batteries are designed to give their best … (marketing may say good until last drop… but if your demand requires a big gulp might not be good enough for your implementation).
My response of “not quite true” is not an attack of the veracity of your statement, but rather, there are far more nuanced responses depending on the needs of the OP question - “how many batteries do you guys bring with you?” … Based on competition setting - with V5 batteries you can manage with 2 minimally with competent charging management.
The true answer is it depends - what factors matter? - # motors, average load on system (which poor build quality can influence - friction is not your friend!), time between matches…
Competition settings can change from venue to venue… and it also matters how much you plan to practice between matches, and access to skills field.
End of the day, running on practice field non-stop before bot stops should let you know how long you can operate on a particular battery. Pro-tip - keep records for each specific battery - that data will serve you well. Label each battery, and take a battery medic checkpoint to see how all the cells are performing.
as they say - “your mileage may vary”… so teams that keep their batteries in a trailer before competition may have different performance.
Last advice to teams - collect data and document as much as possible in terms of factors that impact your robots performance.
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As per the following article: https://kb.vex.com/hc/en-us/articles/360035590552-Planning-V5-Battery-Charging
It takes the battery approximately 1 hour to charge fully. As for us in VEXU, we usually drain from 100% to around 20% because we have a lot more motors. This means that if we assume 3 matches per hour, that is about 3-4 batteries on deck to be charged, and a fourth on the robot (one extra charging for emergency pretty much).
Since you are in V5RC I would suggest 2-3 charging, with the 4th on your robot, assuming 3 matches per hour and you drain your battery every match, to play it safe.
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While I do appreciate your experimentation in this matter, I do have a critique:
That is a pretty significant thing to gloss over. While it is quite difficult for an organization to conjure this data on batteries, it is vital for a study of this kind.
May I ask how old these batteries are? And roughly how much do you overcharge/mistreat them?
Could you share the data you collected with us? If it’s good, it would be a nice resource for the community. (And it could be my AP Stats project… 
)
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I no longer have access to the data, our notebooker from last year has graduated. The reason I did not take into account diagnostic information or age of the battery is that there is not much I can do about these facts.
The batteries were at the school as part of program our university runs to teach elementary and middle schoolers about robotics. I don’t really know how to measure how much a battery is mistreated. Additionally, it’s not like our team will be running the diagnostic on several different batteries to see which ones we should use for the next match.
While I would share the data, our notebooker who was the one that actually recorded the data has graduated, so I do not have the data otherwise I would share the data. I will try to reach out to her sometime this week to see if I can share it here.
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I was not actually expecting this many responses and what seems like a full out debate over engineering ideas on this post. Thank you all for proving that 1 battery will not work and really my question was based on like seeing if people actually bring backup batteries or if they are not required. Also due to me not knowing how to quote specific replies, would anyone know whats the best way to test how long the robot can run with 1 battery? Would it be better to do circles of the grid or just take it out to a 200m strip and just do laps there.
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If you are wanting to test its life on the field, I would recommend you run some matches with your sister teams (if you have any). If not, just practice normal gameplay with the occasional running into the wall.
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You have kind of answered your own question here. If your robot can last for hours moving back and forth, it doesn’t really help you in a competition when it will be doing much more, run through the motions that your robot will be doing on the field over and over. That should give you a good idea
But to answer your original question, we usually bring about 8-10 batteries (stealing from the school’s CTE clawbots 
).
To test how long they would last, like @Micahy321 said, just run a scrimmage for as long as possible.
Our driver while just driving usually gets 20-30 minutes off of each battery, but it goes down to about 4 minutes when you start doing gameplay.
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I would say 4 minutes of battery life isn’t very good… Wonder if this is VEX’s plan to make money - 
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I imagine this is one of the many ways, yes.