Batteries not charging

I need some serious help at the moment. My team and I are not sure if it is the batteries or something with the Cortex / Joystick but the batteries seem like they are dying very quickly now. We tested all thr batteries with a DVOM and they were all reading 1.2V or higher except for one that was at 1.14V but the computer says they are so dead that we cant even download our code. We have a tournament this Saturday and we really need to get this fixed. Has this happened to anyone else? Does anyone know how to fix it or do we need to send the entire unit in?

I assume you are talking about the batteries in the Joystick. Does the joystick linkup with the cortex? Do the leds on the joystick come on? Any chance a battery is in backwards?

You have a couple of options.

  1. Get some Alkaline AAA batteries and try them.
  2. Tether the joystick using the USB A-A cable.

If you are using EasyC (and I assume you are as RobotC does not care about joystick voltage) you can disable the vex system check and it will allow download if the voltage is low. What does the download window say the voltage is?

If my assumptions are wrong post back.

We are using EasyC V4.
The Joystick and Cortex have no problem syncing.
We are using the AAA Vex Rechargeable Batteries in combination with the Vex Battery Charger.

Sometimes we will pull batteries off the charger (freshly charged) and put them into our controllers and we test our autonomous 3 or 4 times and then they are dead.

This gets really frustrating and today we had to stop our progress on autonomous simply because we didn’t have any batteries that were charged.

We really hope that this doesn’t happen during our tournament this Saturday. Looks like we are going to have to stock up on AAA’s if this problem persists. :confused: If anyone can help or knows something we can do please help us!

Devin B of 569C

I do not think that your batteries are actually dead. If you are reading a good voltage on a multimeter, try some new storebought AAAs and see how long they last. When using run of the mill batteries, our controller lasted for an hour and a half on average. Using good batteries (sony enloops seem to work great), the controller lasted for around 3 hours.

To rule out the joystick having a fault I would suggest measuring the current that it is using. Put your multimeter in current mode (A), you will probably have to move one of the test leads to a different input and then carefully (and I mean take your time) lift one battery and connect the meter between the battery and its contact. My joystick (with VEXnet running) measures about 250mA but anything less than 400mA is probably ok. If you have a similar reading then either you have one or more bad batteries or your charger is not charging them properly. If you do have battery/charger issues then I would suggest you take the environmentally incorrect decision and use alkaline this weekend, one set of 6 will last 5 or 6 matches, I bought some Rayovacs today, $8 for 24. If the joystick is using an abnormally high current try changing the WiFi key, if it is still high report back with the reading (or perhaps call VEX tech support).

Edit: I just realized you are going be to at the Granada Hills competition, our teams will be there also, come find us if you still need help on Saturday.

This will probably be better that Devin C does this stuff because idk how to use the volt meter or anything. He is better with that kind of thing.

And yes we are going to the Granada Hills Tournament. Hopefully Devin C and I will be able to come by your table and say hi and whatnot.
Anyways I will make sure that Devin C sees this.
And good luck Saturday!

We are calling VEX support today to try to find out what exactly may be wrong with our batteries but we will for sure stop by at your teams pit and good luck this weekend.


Sounds like a few of your batteries are not holding the charge properly.
I would reccomend you to purchase a new set of recharchable AAA batteries, I believe its ok if they are not the “VEX-brand”

Also at most competitions the teams get the option to simply power up their Joystick using the VEXnet Joystick Power Adapter connected to the field.