7.2V NiCd Battery Substitute

[Dave K.]

For teams operating one or more cameras, servos, or other electronics powered from the 7.2V NiCd battery, and who don't necessarily want to power these loads from the main battery by way of the requisite build-it-yourself IFI charging circuit... I wanted to share some test results.

I purchased four Tenergy brand, 2100mAh, 7.2V NiCd battery packs for about $9 each. After charging the batteries with a smart charger, I discharged the batteries with a programmable DC load set to 500mA and periodically made note of the terminal voltage of the battery pack.

After two charge/discharge cycles, each of the battery packs showed pretty much the same capacity and easily provided 3 hours of use before reaching a discharged state of 1.0V/cell (6.0V). In other words at roughly 2.4 times the current of a 10 Hour discharge rate, the batteries produced better than 1500mAh of capacity.


Information you may not be able to find online:

Weight: I measure 11.5 oz, some websites claim 10 oz.
Battery Size Type: Sub-C
Overall Size: 5.25" long, 1.81" wide, 0.92" thick.
Battery pigtail length: 5.0" (measured from top of pack to tip of connector)
Connector type: Tamiya

The mating connector can be found at Radio Shack, P/N 23-444. This is a "repair kit" and contains both connector sex's with short leads and butt splices. Online and local hobby stores also carry this connector. Thus far I have been unable to find any electronic components distributor that stocks a compatible connector.

Some website URL's links to sellers:
http://www.batteryjunction.com/twoni721bapa.html
http://www.batteryjunction.com/oneni721bapa.html
http://www.onlybatteries.com/showite...t1=12&uid=1010
http://www.megabatteries.com/item_details2.asp?id=13679
https://www.all-battery.com/index.as...ROD&ProdID=434

These are toy battery packs, so you should be able to find these, or one of a very similar make, at local hobby stores or other online retailers. Capacity claims for similar sized batteries range from about 1500mAh to 2100mAh.

Radio Shack P/N 23-036 is a kit consisting of a 2000mAH 7.2V NiCd, a 1000mAh 9.6V NiCd, and a charger. If you are looking for a 9.6V rechargeable battery to make your operator interface portable, and get a higher capacity battery for your robot's backup battery, this might be a quick option that you can find locally. The mating plug for the 9.6V battery should be 23-445.

Remember, for the FIRST competition you may substitute any commercially available, 7.2V, NiCd battery pack. At competition it must be charged with the charger supplied in the Kit-Of-Parts (or by the build-it-yourself IFI on-board charger).