Home  Sources  Part descriptions  Electrical parts  Passive components Resistors Resistor part codes Capacitors Capacitor part codes Batteries Batteries compared  Semiconductors  Integrated circuits  Packages  Mechanical parts  Misc. parts Assembly descriptions   BEAM Pieces is a BEAM Reference Library site.		Batteries A usage guide Most BEAMbots are solar powered, so batteries aren't a huge issue. Some BEAMbots, though, have sufficiently-high energy requirements that they really have to run on batteries. This basically means heads and walkers. When you've made this decision, you now have a couple of ways you can go: Connect enough small batteries in series to reach your desired voltage Use one 9V battery, along with a voltage regulator, to output your desired (lower than 9V) voltage. You'll pick your batteries based largely on what's available (given your budget), whether your 'bot will be recharging the battery from solar cells (if so, you'll want a fairly low voltage battery), and how big your 'bot is going to be (9V batteries are none too light).   Battery chemistry A number of battery chemistries are available. The following comparison chart comes from the January, 2002 issue of Embedded Systems Programming: Chemistry Vnominal (V) Max. load current (C) Energy by weight (Wh / Kg) Energy by volume (Wh / L) Operating Temperature (deg. C) Rechargeable? Life cycle (recharges) Shelf life / self discharge Alkaline 1.5   150 375 -20 to 55 No   5 years to 80% NiCd 1.25 >2 45 - 80 125 -40 to 60 Yes 1500 20% / month NiMH 1.25 0.5 - 1 60 - 120 180 -20 to 60 Yes 500 30% / month Lithium Ion 3.6 1 100 270 - 325 -20 to 60 Yes 50 - 100 10% / month Lithium polymer 3.7 0.2 120 - 160 230 - 270 -20 to 60 Yes 500 10+ years Lead acid 2 0.2 30 80 -20 to 60 Yes 200 - 500 5% / month Zinc air 1.4   300 1150 -20 to 60 No   3-12 weeks to 50% Silver Oxide 1.55   130 500 -20 to 60 No   2 years to 84% Note that here load current is expressed in units of C (which is just the Amp-Hour rating of the battery divided by 1 Hour).   Battery availability A number of types of small batteries are available to us: "Button" cells -- 1.25V each; alkaline or NiCad; these are the smallest in size, but also have a fairly low energy storage capacity AAA -- available in alkaline, NiCad, NiMh AA -- available in alkaline, NiCad, NiMh "9V" -- available in alkaline, NiCad, NiMh; you'll need to use a voltage regulator to get the output voltage down to something CMOS can stomach (usually, 5V). 9V battery cells -- alkaline only. 9V alkaline batteries are made up of 6 clustered cells in a can. You can pull open this can (carefully) with pliers to pull out the small cells (which are a bit smaller than AAA batteries). Since these aren't rechargeable, I don't use them much. Cordless phone batteries -- these are easily salvaged (and in high availability, if you go through cordless phones as often as I do) NiCad batteries -- most output 3.6V, which is just right for most BEAMbots.   To put things in perspective, I have a page comparing charge capacity, size, and weight for basic cells (AAA, AA, 9V) of differing chemistries here. For more information... Analog Devices has published an excellent writeup on Lithium Ion batteries, and how to charge them ("Designer's Guide to Charging Li-Ion Batteries." It's mirrored in PDF format here.
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