@圈仙One PX32, E164, V164PX, TR 164, HM-4N, 4NR52 or 1404M 5.6 Volt mercury battery.
Works with today's alkaline replacements. My Electro 35 has a 4LR52, EN164A, A32, PC164, TR164A, 1404A alkaline in it. These are made with four stacked LR52 or 640A-P cells in series.
The specifications for today's alkaline battery are 335 mAH, 25.5g, 17.1mm diameter, 44.9mm height.
You can use a more common, smaller (170 mAH lithium, 150 mAh alkaline) PX28 if you jam in an extra spring and wrap the smaller battery in something to keep it centered in the Electro 35's larger battery hole.
The correct PX32 costs only $9.99 and lasts twice as long as the wrong $8 PX28 that doesn't fit without a kludge, so order two PX32s and keep the spare handy so you won't have to pay $15 for a PX28 at retail if your battery dies.
![](http://tb2.bdstatic.com/tb/editor/images/face/i_f25.png?t=20140803)