Using only one battery

Recently my team has been talking about using one battery to power the entire robot. In the past, we have always stuck to double-battery designs, but we’ve noticed that in a single match we use less power than is held in only one battery. We’re wondering if anyone has tried using a single battery to power their robot, and if there were any major side effects? Would we be able to power a robot that is roughly 10 pounds and uses 8 high speed motors without any major slowdowns?


Normally the second battery isn’t required as a result of total power consumption over the course of the match, but rather to spread peak current across two batteries, reducing the voltage drop due to the battery’s internal resistance. Using the power expander will also spread your current across more circuit breakers, thus allowing for a higher peak current draw.

That said, most teams that I have seen don’t use a power expander… they might like to, but not have the resources… or they simply might not need to.

So yes… lots of teams get by just fine with one battery… but that doesn’t necessarily mean that your robot will. What matters is peak current draw which is governed by how many motors are active AT ONE TIME, and how much current each of the active motors draws. As motor current draw is directly proportional to torque, having many heavily loaded motors will obviously draw more current than having just a few active, lightly loaded motors.

The easiest way to test this on your robot would simply be to unplug the motors from the power expander, and plug them directly in to the cortex… then play a practice match or ten.


I have always used one battery on my robot. In fact, last year, when I experimented with a power expander, the drive actually ended up stalling more.

We try to use exclusively one battery as well. The added complications with placing the power expander and the extra battery aren’t worth slightly more run time and we haven’t noticed any significant increase in time before motors stall out.

Furthermore, weight is even more important this year than before, and the extra pound or so hurts in every aspect of the game. (Driving slower, hanging slower or not at all)

I am using one battery for the sake of keeping my robot as light as possible, and I feel that for a 2 min match there is no problem. As long as you have a fresh battery for every match it should be fine. The voltage drop on a Nickel metal hydrate battery is not linear, it drops very little constantly for some duration, and then it really starts to fall. By then though, the match would be over.

My team used 2 batteries in gateway and sack attack, but we now only use 1 - mainly since we keep forgetting to put on a power expander. We’ve done fine with 1 battery, winning several tournaments and an excellence.

The only real issue we’ve noticed is that playing two matches with the same single battery isn’t a good situation. Our bot needs a new battery every match in order to avoid significant slowdown. We could do two matches with the same pair of batteries quite easily last year.

We use two batteries for the extra 4 Amp fuse in the power expander. Having that extra breaker and wiring it accordingly should (in theory) make the different sub-systems die less frequently.