Hey Ben
The lead acid battery you used on the robo luggage was kinda silly, or maybe just a bit of an anachronism. So here is what i would do: Order a bunch of li-ion cells from, say, sparkfun, wire them up in a 3s2p configuration and hook the in-between-the-cells-wiretaps up to a small AVR. You would then program the AVR to monitor the cell voltages and cut off charge or discharge current in case of cell imbalance or over- / undervoltage. You would then build a Charger which would basically be a voltage regulated power supply (12.6V) with a suitable current limiter (1C normally). Oh, and the AVR would also do some nifty cell balancing during the last phase of charging by engaging some shunt resistors in parallel to the cells.
At this stage you would simply have reproduced what is implemented in each and every laptop battery ever made. But it would be your own and really, really cool. And it would be open source and would find many, many uses for when people need to have more than 4.1 volts in a portable gadget.
A milder variant would be so just make an external charger with the above mentioned characteristics and custom-make a blade connector to connect to an existing laptop battery and read out the interesting stuff via the SMBUS, from the raspberrypi for example... Or you could make that first and in a second show build the smart li-ion battery. This way you would make the embedded AVR understand SMBUS-smartbattery commands, so it could even be connected to an actual laptop in the voltage and such would get reported to the host computer. Well maybe a bit over the top.
Anyway, the reference implementations of the bz90z20 and similar ICs are really interesting.
Check out the attached photos - that's what i meant by custom-made blade-connector, the battery is from a dell laptop, i used strips taken from a tin can.
And BTW, de-mystifying laptop batteries is a good thing anyway.
And you might also make a mention to the way multi-cell batteries are handled in the realm of RC-models.
You could even make another show where you hack an old 12v Ni-Cd driven hand-drill to run from salvaged laptop battery cells. I once did that very crudely when i discovered that the old hand-drill i borrowed from my mom had a completely dead (20+years old) battery and I absolutely needed a drill, see the third photo. This is not the way to do it though, because there is no undervoltage protection. But that is where your show comes in ;-).
sorry for the long post.
I totally love your show BTW. The "Argh, too much light" episode was right on. ;-), the essence of scratching an itch, me thinks.
Greetings
Matthias
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