So, my team has been having a problem with our robot battery that no one can fix so far. After driving our robot for about 30 seconds to a minute, our robot light turns red and our robot stops working. We have repeatedly tested the battery voltage afterwards, and it reads fully charged, or close to that. We have replaced the brain and the battery cord, but the problem persists. We have nothing in our code that could mess with the battery and brain. We need an answer before Feb 11th, as that is our next competition. Thanks!
Could it be a loose connection between the cortex and the battery? Or did you already try this when you said:
How many batteries do you have access to? Maybe the battery you are using has worn out. Normally, this happens to old rechargeable batteries as a result of many charges, but if you use the “fast charge” option when you charge batteries you could actually be speeding up the aging process of batteries.
When your cortex’s battery lights go to red, what exactly happens to the robot? Does it completely stop, or do the motors seem to be running with less power, or do you lose connection completely?
I think the first thing you should try is test with another battery and see if the problem persists.
Testing a battery’s voltage without a load is problematic. Try another battery.
Also, are you using black VEXnet keys, or white ones? If you have black ones, try driving your robot on a tether cable and see if the same thing happens. The normal failure indicator for black VEXnet keys is the dreaded slow-flash-red light, but it is something else to try.
Yep, loose battery connections are definitely something to test, as they can ruin your scrimmage game pretty quickly. If you discover this is the issue, consider getting some battery extension cables as it will stop you from having to use the port on the cortex as much. We have also found that the ends on the cables in our experience make a much nicer electrical connection and hold the battery connector in place better (esp with the provided clip).
I am highly towards the loose battery connection. But if it’s not that, maybe the motors are drawing a mass of power, causing the CORTEX to stop. Did you try having a power expander? Did you try seeing if it’s fixed when adding a 9V? Did you try changing the gear ratios to be more torque?
Adding the 9V shouldn’t effect anything, it is not used for motor power. It is used to maintain VEXnet connection, if I remember correctly. The situation definitely sounds like a loose battery connection. The connector in the Cortex often is the weak link. I don’t allow any of my teams to plug their batteries directly into the Cortex. They MUST use the battery extension cable.
“our robot light turns red” That’s why I suggested the 9V 
But it may most probably not be the issue though. If EVERY light turns red, probably it’s an issue with the CORTEX or battery, and most probably the battery is the one having the issue. Have you tried replacing the battery before trying again, because usually all lights red means that the battery could be damaged or one of the cells are corrupted/not working.
Our bot starts losing power really early in the competition, even though the batteries are fresh off the charger.
We have a similar issue where we eat through batteries very quickly, turning yellow after 30 seconds of driving, then red after a couple of minutes. We’ve ignored it for the most part because the robot can last through a match pretty easily, but it sounds like your robot goes through batteries even faster. Can you post your wiring here?
Not really. I don’t have a camera, and I can’t bring the bot home
I mean like what motors go where in the cortex.