Using VEXmotors to reverse charge V2 battery packs

One of the things that happen across the upcoming holiday break is battery packs are left in the robot.

Because there isn’t an ON switch (switches are all soft) the CPU wakes up and say “Hey didja push me?” “Nope, back to sleep” and this cycle repeats over and over. In a long wait it’s like " um ah did I feel a sli…ght push. ok, nope, gonna enter a battery coma here"

When roboters return from break the brain will not power on, chargers won’t charge (dreaded red/green flash sequence). In the V1 times you hooked a motor to port one, attached a gear and spun the gear 30 time. This added enough voltage to the battery to get the charger to accept the brain and charge it (note, if this happens it takes multiple charge cycles to get the battery fully charged.

I built a device with a motor and the knob from the crossbow to make this easier. Knob to motor, spin, count 30 spins all set.

With last year’s mess of battery issues, I built a motor spinner

Brain to drive motor at 50 RPM for one min and it’s connected to the “generator” motor running at 50 RPM. Cable from this motor goes to the dead/battery/brain combination. Hook it up, press run and for 60 seconds it feeds the other battery. Put it into the charger and let it charge. (Cases where one cycle don’t work, try two, but I’ve never had a battery come back to life after 2 or more cycles)

I have about a 99% success rate. Please note that you’ll need to charge these “vampire” battery to full charge, let them cool off for 2 hours (someplace cool please) then charge again. My charging station is a granite slab that stays about 55 degrees in the robot lab. Your cooling time may very.

Which now brings me to the new VEXIQ battery packs. What should be my plan to revive dead battery packs?

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That’s not how it works.
The brain should not use any battery power when off.
pushing the button enables power to the cpu which boots and then activates a FET to keep power on.

The IQ generation 2 battery pack will go into deep sleep after 24 hours (IIRC, it may have been increased to 72), you then have to push the button on the pack to wake it up again. I would not leave them for a long period fully discharged, but leaving a partially charged battery on the robot for a couple of weeks should be ok.


OK, help me understand why a brain that has a fully charged V1 battery pack on 10 December at the start of the break has a fully discharged brain on the 6th December they return. Or the simlar, robots end in Mid-may and by labor day the battery pack is dead. The general leakage current of a FET is micro amps.

My assumption (because I don’t know for certain) is that it’s just self discharge, something all batteries suffer from. Gen 1 battery packs are NiCd and can (according to google) suffer from self discharge of up to 25% per month. I have older (4+ year old) Gen 1 packs that just won’t hold much charge anymore, if I don’t use them for a couple of weeks they die. I’ve not noticed anything like that with the new packs which are lithium-ion.


OK, I have 4 year old Gen 1 packs that seem to do Ok, but I keep them on a charging regime. I’ll be interested to see what happens to my first crew (over 10) battery packs across the holidays. Thanks as always for your help.

My experience is the old Gen1 (NiMH chemistry), if you discharged them so low that you needed to do the back drive motor trick to bring them back alive, they are not going to be good as new. I marked them so my team knew only to use them for practice. I had the luxury of running them through a battery discharge tester to graph their performance, new vs old battery performance is significant. Gen2 hasn’t been out long enough for me to pick up a trend, but the Li-ion chemistry would point to it’s not a concern anymore. (although the safety circuitry will not let you back-drive / charge the cells, that’d be a no-no with Li-ion).


I have both a that I use. Back in the day I got a battery beak Battery Beak - CTR Electronics and broke apart a charger to get to the contacts

Both have been helpful in looking at battery charge cycles. I do other things with battery packs other than robotics and it makes a big deal to dig into the cells.

Hats of to James for the Battery Doctor for V5 an I assume the same for the new V2 battery packs for IQ. Being able to graph packs from best competition to good for practice is a game changer for teams. The issue is the time to test and the willingness to track the battery pack. Thanks @mbeem for your experience with battery packs.