Large Backup Battery

Our team is using AndyMark Super Shifters this year with servo shifting. I’ve read here on CD, and found out through testing that the servos drain the backup battery very fast. My question is are we allowed to take 12 NICAD cells and wire it so that we get 7.2 Volts, but twice the milliamp hours? (6 parallel pairs in series)

I know its not legal to use 2 batteries, but I believe this would be considered 1 battery.


According to <R73> any commercially supplied 7.2V NiCad may be substituted for the supplied backup battery. Your question appears to asking about making a custom backup battery of some sort which I would say is not legal. Purchasing a 7.2V NiCad with a higher capacity does appear to be legal and would likely be the best solution to pursue.

<R73> The 7.2V Robot Control backup battery shall be connected to the Robot Controller as
described in the Robot Controller manual. The 7.2v “backup” battery is considered an
integral part of the Robot Controller, and shall not be used for any other purpose. The 7.2v
battery should be charged to at least 7.0v before entering a MATCH. As a replacement for
the FIRST-supplied battery, any other commercially available 7.2V NiCad battery pack may
be used.

emphasis mine

In the past, the backup battery, regardless of capacity, needed to be charged with the KOP charger, or the custom circuit designed by IFI. This no longer appears to be the case. PLEASE VERIFY WITH A QUESTION TO THE GDC!! I would hate to steer you in the wrong direction.

<R49> The 7.2v backup battery may be charged on or off the ROBOT. When off the ROBOT, the
battery is to be charged with a 7.2V backup battery charger. When mounted on the ROBOT,
the backup battery may be charged from the 12VDC primary battery by using the custom
charging circuit available from Innovation First Inc. or any similar charging circuit (note: IFI
will provide the design for this circuit on the IFI website, however teams must obtain the
parts for this circuit and assemble it themselves). The use of this circuit is strongly

(Partially) Not true, the wording of the rule you have quoted is exactly the same as last year’s manual. Last year it was allowed and even recommended by posts here to use a “smart” charger instead of the supplied KOP charger.

I know our team had an issue last year with a fried backup battery that we believe may have been caused by overcharging using the KOP charger.

By saying “in the past” , I intentionally did not point to a specific year. (Look at the rules for 2006 and you may just see that I am correct.)


Why Not Build A Backup Battery Circuit? Sorry For The Weird Text, I’m Doing This On My Phone…

Going out on a limb…NO. Never parallel batteries.
You can buy larger capacity battery packs from places like Digikey. You can also use the IFI onboard charger (although I don’t personally recommend that). I believe Digikey has packs up to 1100 maHr.

Is your recommendation against the onboard charger based on the specific design of the IFI charger or the concept in general. The rules allow for a “similar charging circuit”, perhaps if the recommendation is solely based on the IFI design someone should design a better one and put it up as a whitepaper?

thank you all for your help.

I asked our electrical guys if we could put a backup battery charger on our robot. They told me no because under heavy load, the backup battery would attempt to charge the main battery. In 2006, they used a slightly modified one and at the regional, they were told it wasn’t allowed.

The rules this year give teams the option of designing a series diode into the input of an onboard backup battery charger circuit. That solves the problem of the backup battery attempting to power the entire robot.

So far as I know, we aren’t using the backup battery for anything besides the control system backup power. Still, we’ll be using an onboard charger just for the convenience of not having to remove, recharge, and replace it.

The answer would be no, the backup battery charger wouldn’t supply current to the robot in brownout. The RC goes to sleep when the main input falls below 8 volts for a period of time. 7.2 volts isn’t enough to wake it up.

As to my other post…There is no substitute for having a second, fully charged backup battery to put on the robot before sending it out.