Sputtering 9920 and hot caps

[BrianG]

Well, like I said, caps should never get hot. Assuming they are still in working order, I can only assume the rest of the circuit is quite hot and the caps are heating up simply because the leads are on the same circuit traces.

They could also warm up if they are charging and discharging at high currents. The batteries charge them up, but then extremely high currents cause the battery voltage to sag and the caps will discharge as fast (and with as much heavy current as the circuit will allow) as possible to compensate. Then, when the load goes away, the batteries continue to supply the load and charge the caps again. This high current charge/discharge could heat them up.

Sometimes, it may seem that electronics are weird, but it all makes sense once the mystery is solved.