I purchased 6x 2.7 volt 400 farad supercapacitors from
Digikey for $77.66 including shipping
Above 400F, the price of the capacitors skyrocket.
Trying to keep cost down as much as possible, I used 12awg wire that was already on hand to create the very short series connections and the 6" positive and negative leads. The positive and negative wires were cut to slightly different lengths to reduce the chance of accidentally touching them together.
I wonder how many amps I can safely push through these 6" 12AWG wires?
After soldering everything together and using duct tape to crudely hold the 6 cells together, I charged the whole series of capacitors up to 13.5v using an RC battery charger. Initially the charger delivered 7+ amps, but as voltage of the capacitor series grew, the amps plummeted until I cut charging at about 30mA. While the charge took place, I used a voltmeter to periodically check each cell for balance. At full charge, the cells maintained extremely close balance.
The Honda Rancher ATV was the first vehicle tested. It has a parasitic electrical load of 0.5mA, which is extremely low. The capacitor series alone should be able to replace the battery. Since it has a pull start as a backup, there is no danger in depleting the capacitors.
After removing the suspected weak battery and replacing it with the capacitors, I turned the ignition on, verified 13v, and hit the starter... click. That was all I heard. The voltage held steady and my ammeter registered a max draw of 4 amps. It looks like what my dad thought was a weak battery was instead a problem with one of the brushes on the starter motor. I pull-started the ATV and watched the capacitor voltage climb to 14.5v and hold steady.
Since I didn't have time to get the ATV working to test the ability to run on capacitors only, I moved on to Lafawnda (the Honda motorcycle). She had a measly 1.25mA parasitic load. Another great candidate for battery replacement, especially since she is a performance machine and responds well to loosing just a few pounds of weight.
I accidentally blew the fuse on my RC charger, so I attempted to start Lafawnda on the 10v remaining charge from the capacitors.
Well, she started with just 10v and drew a peak of 77 amps! I don't think it would have started with much less than 10v.
I have measured my Dodge/Cummins at over 400A peak when cranking, and I'm not brave enough to even put the capacitors in parallel with the 2 weak starting batteries for fear of melting the leads or hurting the capacitors. I might build up the courage after completing more testing, including starting the TSX.