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| Can I use rechargeable batteries in the RCX? |
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The short answer is yes. Alkalines are preferred, but you can use rechargeables. However, there are several disadvantages of which you should be aware.
Disadvantages of Rechargeables:
- Most rechargeables, when fully charged, are only 1.2V instead of 1.5V. Thus, six batteries provide the RCX with only 7.2V instead of the 9V that alkalines provide. The RCX turns off when the charge is less than 6.5V, so you only have about 0.1V to lose in each of your batteries before the RCX turns off.
- When the voltage of rechargeable batteries drops off, it continues to decline at a quicker rate than alkaline batteries.
- Rechargeables tend to loose voltage at about 10% per month when they are just sitting on a shelf, depending on the type of battery.
- Not all rechargeable batteries are the same size and shape as alkalines - they vary in length and in the shape and position of their positive contacts.
- Because you will be changing rechargeables more frequently than you would change alkalines, more opportunity for the RCX firmware to be lost or corrupted is created. (When changing batteries, you might want to plug a \"plug pack\" into the RCX so you don't corrupt or wipe your RCX's firmware. Radio Shack sells an inexpensive 6xAA pack with a 9V clip on top and a cable that plugs into the RCX.)
All that said, some RCX users are successful with rechargeable batteries, and they save money and waste! Here are the issues to consider before purchasing rechargeable batteries for your RCX:
Type of Batteries:
- NiMH (Nickel metal hydride) - Most common, seem to be most consistently the correct size for the RCX
- Rechargeable alkaline - Ideal, because they are 1.5V when fully charged. But they don't last as long as normal alkalines and have a limited number of recharges.
- NiCad (Nickel Cadmium) - Not recommended, as they have a chemical memory effect.
- Other - Eneloop batteries have long shelf life, and are worth looking into.
Size of Batteries:
- Because not all rechargeable batteries are the same size as alkalines, we strongly recommend that you verify the physical size characteristics of any rechargeable battery brand before you purchase in quantity.
- Try a "battery snugness" test: take off the RCX bottom and gently shake the RCX. If any of the batteries fall out, they are not the correct size, and you'll need to purchase a different brand of batteries.
Charging of Batteries:
- For optimum performance, rechargeables should be charged in the same group or pack in which they will be used. In other words, if you use six rechargeables, they should be charged together and used together to prevent uneven discharging and sudden shutdown of the RCX.
- Unless your rechargeable batteries are charged and discharged at the same rate over the same time, they build up a chemical memory. In a classroom where you may have 60 batteries and a number of 4 battery chargers, you will find that they are being charged and discharged at different rates. The result is that one battery will decline more quickly than the others, and the RCX will turn off sooner than you expect.
Downloading Firmware:
- The best method for downloading firmware is to have the RCX powered by an AC adapter plugged in to the wall electricity unit.
- If you are having trouble downloading firmware, either with rechargeable or non-rechargeable batteries, switch to an AC adapter for RCX power.
Troubleshooting:
- If you find that you are losing firmware all the time or that the RCX is suddenly shutting down, it is likely that your batteries are not the correct size and thus are losing contact with the connections inside the RCX battery case. Use a different brand or switch to alkaline or the AC adpater.
- Some people use electrical tape to secure the batteries in the RCX. However, if you have to tape in the batteries in order to keep them in the compartment, chances are very good that any physical change in orientation of the RCX during the build process or operation of the assembled robot could cause unexpected shutdown and loss of firmware.
- When changing batteries, you might want to plug a "plug pack" into the RCX so you don't corrupt/wipe your RCX's firmware.
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