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For the first time builder, knowing a bit about providing power for your robot can save you from a mountain of guess work, headaches and maybe a few valuable dollars at the same time. At present this page is far from complete but it will give you a start on choosing batteries for your robot. More information is being compiled and this page will see more updates soon.
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Batteries Not Worth Thinking About SLA's Ni-Cad's Ni-MH Battery Tips
Batteries not worth thinking about.
First off, forget about pulling the lead acid battery out of your car or your neighbors motorcycle. Even though they are inexpensive compared to the amount of power they can deliver, most events will not allow them. This is simply due to the fact that if a conventional lead acid battery is damaged or tipped over, sulfuric acid becomes spilt and will make a serious mess of the inside of your combat robot and is very hazardous to clean up when sprayed across arena floors. As for the typical alkaline battery, these are not rechargeable and would rapidly become a much more expensive option since you would have to replace them far to frequently. The use of lithium based batteries is possible as they can be recharged and have an outstanding power to weight ratio but.......very very expensive and they require expensive equipment for recharging. If you do have unlimited financial resources, then definitely go for the Lithium-Poly batteries available at Radio Control hobby stores. If you don't have a bucket of cash to spend on batteries then here are your options.
Sealed Lead Acid batteries are not like the typical lead acid battery found in cars and motorcycles. SLA's have a either a matting material that is inside the battery that holds the liquid acid (aka: electrolyte) and prevents it from spilling, or in some cases chemicals have been added to the electrolyte that turns it into a gel. This type of battery has the advantage of being the least expensive option and charging equipment is quite inexpensive. The disadvantage is that they are the heaviest of the battery types for the amount of power that can be drawn from them. Avoid regular cycle SLA's and look for "Deep Cycle" batteries. Draining the power from a battery till it is dead or nearly dead will damage it. Regular cycle batteries can only handle being drained 5-10% a few times before they are damaged to the point of no return. Deep cycle batteries can be cycled (discharged) to as much as 30-45% of capacity depending on the manufacturer before suffering the ill effects of being drained to far.
Nickel Cadmium batteries are very common in combat robots. They are more expensive than SLA's and Ni-Cad's also require special charging equipment. However the advantage is that they are readily available from a number of sources. You can build or by packs of batteries to meet the power demands of your combat robot. Charging equipment for Ni-Cad batteries can be obtained at R/C hobby stores and over the internet. A typical charger will cost around $100, but be aware that most of these chargers were designed for use with R/C equipment and run on 12volts DC. You may need to purchase a power supply for your charger. Some computer power supplies will do the job quite well as a power supply for your charger. Another advantage to Ni-Cad's is that with a good charging system these batteries can be properly "cycled" or drained and recharged, which will help keep your batteries in good condition. You should be able to get 300 - 500 cycles from a well sized battery pack. Ni-Cads should only be drained to about 70% of capacity and if possible avoid tossing them onto a charger immediately after using them. All batteries can be damaged when they become hot from rapid discharging and recharging. Give your batteries a chance to cool after you drain them and after you charge them. Another disadvantage is that Ni-Cad's contain environmentally dangerous metals and must be disposed of properly.
Nickel Metal Hydride batteries have been around for a while and continue to come down in price. They are more expensive than the Ni-Cad batteries but have the advantage of packing more power when compared to weight. Like the Ni-Cad battery a special charger is required, fortunately many of the R/C battery charger systems on the market will handle Ni-MH batteries as well. With proper care Ni-MH will deliver 600 - 800 cycles. Many manufactures claim a much higher number of cycles but in the world of combat robotics, everything tends to get pushed towards the limits so don't expect to achieve the high cycle counts claimed by manufactures. Another advantage to Ni-MH is they do not contain the dangerous metals that Ni-Cad batteries do and thus they present less potential damage to the environment.
Do cycle your batteries every 2 or 3 months. A good charging system will do this automatically.
Don't allow batteries to become over heated. Over heating batteries will damage your investment.
Allow batteries time to cool down after being charged or drained.
Keep batteries stored in a cool dry place when not in use.
Avoid allowing the battery pack from being shorted out. A shorted out battery pack can completely destroy the batteries in less than a minute.
Dispose of batteries in an environmentally responsible manner.