I would recommend one also verifies they have 3V at the terminals after installing just the single battery.
I looked at the document pinoosh linked to, tried it, and nada...0V. Verified wiring in the battery holder with an ohmmeter, the single battery should work as shown in the doc.
Re-install the second battery, works fine.
Finally I realize what's happening: the terminals in the empty battery compartment were touching, so a dead short across the output.
So either ensure the empty compartment terminals are not touching, separate them with an insulator, or, just go ahead and install the second battery as mentioned earlier in this thread. You'll have the two batteries in parallel, and you'll be just fine.
I looked at the document pinoosh linked to, tried it, and nada...0V. Verified wiring in the battery holder with an ohmmeter, the single battery should work as shown in the doc.
Re-install the second battery, works fine.
Finally I realize what's happening: the terminals in the empty battery compartment were touching, so a dead short across the output.
So either ensure the empty compartment terminals are not touching, separate them with an insulator, or, just go ahead and install the second battery as mentioned earlier in this thread. You'll have the two batteries in parallel, and you'll be just fine.