This is the information we provide on the Yahoo! Spotmatic group:
Spotmatic Battery Information
The most experienced members of the Spotmatic group have compiled the information below and many of them have been using Spotmatics since they purchased them brand new in the sixties and seventies. This information is being provided so that you do not have to ask about it as a discussion topic on the forum. It has already been discussed and answered many times and there is nothing more to add so please do not ask again. All you need to know is contained in this document.
For battery cap information go to the bottom of this document.
In relation to batteries, there are 5 groups of Spotmatic cameras:
1. SP Series. This includes SP, SP500, SP1000, SPII and SPIIA.
2. SP F
3. Electro Spotmatic and ES
4. ESII.
5. SL. This camera has no meter and, thus, no battery.
SP Series
The 1.35-volt mercury (mercuric oxide) battery originally used in the Spotmatic SP is no longer available due to environmental protection laws.
Replacement batteries available today are 1.55-volt but the Spotmatic uses a "bridge" circuit in its meter, making it insensitive to battery voltage variations. So, despite what you may have read - No meter recalibration is necessary as all Spotmatic SP series cameras can handle the increased voltage.
The alternatives are:
• Spend about $30 for an adapter from CRIS Camera Services (
Digital Camera Repair | C.R.I.S. A+ BBB Rating) and a battery to insert into it. But this would be a waste of money as it is definitely not required.
• Spend about $10 for a Wein Products MRB400 cell (modified Zinc-Air cell). They are quite expensive and have a limited life (about 6 to 12 months) unless you remove the battery after each use and seal up its air hole (it needs air to work). This is not a recommended solution.
• Spend about $3.00 for one of the many 1.55-volt silver oxide batteries available over the Internet, at Radio Shack, most drugstores, camera stores and even some supermarkets. They will last you for about three years if our experience is typical. Make sure you insert it the right way for proper polarity, and take up the excess space in the battery box with a rubber O-ring from the hardware store, that will cost you about 49 cents. You might have to bend up the battery contact in the battery box to make good contact.
• Silver oxide batteries that work are: Mallory PX-400 or RM-400-R, Varta V394, Maxell SR936W or SR936SW, Renata 394, or any type 392 equivalent.
• Do not be tempted to use alkaline battery equivalents as they have a much steeper discharge curve. The silver oxide batteries have a flat discharge curve similar to the old mercury batteries.
SP F.
• Mallory PX625, Duracell PX625A, Excel Z625PX, Eveready E-625N.
• The Spotmatic F uses a dual coil meter movement that, like the bridge circuit, cancels out battery voltage variations on the level we are dealing with here. So it is immune to the difference between 1.35v and 1.5v, too. The original battery for the Spot F was a mercury type. In this case, Pentax used the identical circuit in the KM and K1000, without any electronic changes. They substituted the silver types with NO ALTERATION at all.
Electro Spotmatic and ES.
6-volt Eveready #544, Duracell 28L Lithium.
ESII.
Eveready S76E, Mallory MS-76H, in fact any 76-type battery works -A76, S76, MS76.
Originally posted by pickles 
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