How do I get more battery power

I want to add a much larger battery but I dont want to breack my bot.
What should i do, and were do i get it. Please post pics.

Depends on why you want the bigger battery. Do you want longer battery life or do you want to overdrive your motors?

Longger life time.

For longer battery life, put two batteries in parallel. You can buy a couple of 7.2v battery pack repair kits from radio shack and make a parallel cable by hooking the red wires together and the black wires together. Start off with both batteries charged, and when you charge one battery, be sure and also charge the other one.

You can parallel more batteries for even longer life, but then it’s going to start to weigh too much.

I see what you are trying to say, but wouldn’t adding two 7.2v batteries give the robot 14.4v instead of having it be 7.2 lasting a lot longer? Like AAs the more you add together, the more voltage that goes to the system. Right?

The voltige regulator is in the battory, not in the VEX Micro Controler (the out put on the battory is 7.2 and the VEX is only ment for 7.2) if the voltige regulator was in the Micro Controller (which it is not (i think) then you could completly splice the wires together).

If you connect the batteries in parallel, the voltage stays 7.2. If you connect batteries in series, the voltages add to 14.4

The voltage regulator is not in the batteries, it is in the controller. It reduces the battery voltage to 5 volts for use by the electronics.

In your search for more power you could try usinf the transmitter battery instead. It has 9.6 volts and makes the robot about 1/3 faster and the battery seemed to last longer although we did not time it to confirm this.

Or, you could charge it right before you use it, for example, leave it on charge right after you use it and when it is done leave it out and slip it on whenever you use it, you will find that you will not try and run your robot when it is not needed, saving more battery juice and a full battery will give off more power.

you could always goto larger and more powerful batteries not meant for robotics but you could fry your m/c

There are NiMH digital camera batteries size AA, rated 2250mAH or 2500mAH.
If you put these in the starter kit battery holder, you should have much longer power than the NiCd Vex battery pack. Reliability and IR drop across all those springy connections may be a problem.
There are also battery packs the same size as Vex battery available from Tower Hobby RC website with upto 3000mAH. $10-$70 for 1500mAH to +++.
As long as the voltage is the same, none of these suggestions is going to fry the controller.

yeah I never thought about using AA’s in the battery holder. I have some 24ooMaH AA’s and they last a long time with a higher peak power.


If you read some of the older posts made by the VexLAbs folks, they tell you specifically not to use other types of batteries because of the voltage drops that occur when the Vex equipment is pulling current out of them.

You are right that correct initial voltage means that the Vex gear isn’t going to get fried; but you appear to be implying that all battery types will behave similarly (enough) when put under a load.

I haven’t tested how other battery types work in Vex applications, so NiMH or other types might work most of time. However, the VexLAbs folks had a reason for writing that recommendation I remember seeing in the earlier discussion thread. Consequently I have stuck with using NiCads (from VexLAbs and elsewhere).


They tell you to use the battery supplied because they know it works and there will never be a problem with it but there are other possibilities such as using the transmitter battery in the robot.

You could put the batteries in parallel but couldnt that ruin the mod. by inputing too much amps of current…
i thought it would be safer to hook a relay with a diode so when the battery drops to a certain lvl it auto. switches to the other battery

Batteries don’t push amperage, they offer it.

Circuits (in DC terms) draw current (amps) because they are a path between the two sides of a voltage difference.

Parallel batteries don’t alter the voltage difference across the the robot’s circuits, so they don’t alter the current that flows (because of the voltage across the circuits) through the circuits at any given time.

Parallel batteries, roughly like parallel water towers of equal height, can hold and then supply more energy (more gallons of water); but the second battery (tower) doesn’t change the voltage (water pressure).

In the robot current = coulombs/second and two batteries hold more coulombs than one, so the robot can run longer. In the water tower analogy two towers hold more gallons than one, so you can take a longer shower.


No, you could put a hundred 7.2v batteries in parallel and it wouldn’t hurt the controller; It would just run for a hundred times as long. Now, if you put a hundred 7.2v batteries in series, there would be lots of smoke…

About voltage -
The official voltage specification of the Vex controller is 6-9 volts.
The official voltage specification of the motors is 4.5-15 volts, although they warn of reduced motor life at >9v.

The controller electronics are fully capable of handling the maximum motor voltage of 15v, meaning that you could run a robot off of a 12v lead-acid battery.
The only time this will cause a problem is if you pull enough power out of the digital or analog connectors (center pin,+5V) to approach the maximum rated current of 1Amp. (This is not likely, as most of the things that plug into the digital and analog ports draw very little current). Even then, the most likely thing that will happen is that the voltage regulator will temporarily shut down due to its built-in thermal overload protection.

I would not have a problem using a 12 battery on a Vex system, although I would likely limit the motors to less than full speed to keep from overstressing them.

That sir was a beautiful analogy.

Putting the batteries in paralell does indeed leave the voltage the same. It also doubles the maximum available current which in effect will also increase the power available to your robot. I mention this because it will also increase the chance of a burnout when, for example, a motor is driven to a hard-stop(i.e. unable to move due to a physical barrier).

Also, as mentioned, it also doubles the life of the batteries given the same load.

Parallel batteries only double the instant current to the robot motors if they were the limiting factor in the first place. You can tell if this is happening by placing a voltmeter across the battery while stalling the motor; if the voltage drops at the battery terminal, then doubling the battery would increase the power.
Other common limiting factors are the series pass switches in the PWM motors, and the wires to the motors. If the wires were a problem, then Y cables to run two motors from one motor channel would split the available power.
Regarding burn-out, I wonder how the servos are designed. Will the pass transistor burnout at max current, or merely get hot? Is there a thermal sensor to turn off the pass transistor? If the specs say it is thermally protected, then even if a parallel battery does provide more power,
it will just cause a faster thermal shutdown of the motors,
and not burn them out.

There are lots of reasons for Vexlabs to say that, to lower their liability, ensure a uniform/controlled user experience, (and enhance their profitability?)
I have some other 7.2v batteries, whether NiCd or NiMH, that I wont hesitate to use in Vex if they happen to be charged and I need a charged battery, or just to save the official vex battery for offical FVC competitions.
The Vex battery has 2000mAH printed on it. Tower Hobbies has NiMH “Venom” batteries rated at 3000mAH for $20. If someone is doing long demonstrations (or heaven forbid, real work?), and needs some longer lasting batteries those might be a good choice. Or cheaper Shark batteries, and put them in parallel. Any local RC racing hobby store probably has a good selection as well.
NiMH are good for power tools with heavy loads, so I don’t see why they would be bad for Vex.