The Solar Keyboard’s claim to fame was the two small solar panels on the keyboard that recharged the battery as you used it. Theoretically, the battery would last the life of the keyboard.
In practice, the battery would die after a few years. It could be replaced with a ML2032, which could be purchased online for $5 to $9 each.
My solar panels seemed to be failing to keep the replacement batteries going for much longer than a year, so I decided to experiment with other power sources. I tried some AA batteries in series, and it seemed to work, but it was bulky.
I also tried the CR2032, the same-sized button-cell battery, with the same voltage, but made of lithium, and not meant to be recharged.
Well, surprise surprise, it worked, and it worked for around one year.
Furthermore, I found that, in a pinch, I could recharge a discharged CR2032, and use it a little bit longer. Recharging involved putting 5V across the battery, and cycling between charging for 10 – 20 minutes, and then letting the battery rest an hour or so.
The CR2032 is less ecological, because it doesn’t recharge, but when the disposable battery lasts just as long as the rechargeable, what’s the difference?
Current is More Important
I put a voltmeter across the batteries, and most were still close to 3V, so I thought they’d work OK. It just wasn’t the case.
With both types of batteries, as they ran down, but especially true for the ML, having the light pointed at the solar panels helped keep the keyboard functional.
My best guess is that the current was declining, and the solar panels were making up the difference.
Hacking the Ends Off the Battery Holder
I was tired of trying to pop out the battery holder, so I clipped the ends off the latch that holds the battery in place. The battery now pops in and out without resistance.
To keep the battery in place, I put tape across the holder.