I see that the 6v px28 battery for the Pentax Digital spotmeter is available in silver (original), alkaline or lithium. Can you use a lithium battery in this meter or does it require the silver for accurate operation. (Does it have voltage regulation?) I would go with the lithium as they typically last longer than alkaline and weigh less. Is this also true as compared with the silver battery.

-- Richard Ross (ross@hrl.com), September 25, 2000

Answers

I've been using a lithium (Eveready, with the red end cap - sorry, don'thave the exact model num,ber handy) for about a year with no ill effects. My exposures seem acurate, even in subfreezing temperatures.

As far as silver to lithium comparisons, I can't provide any scientific measurements, but the new lithium battery feels just as light as the silver. I'd expect an alkaline to weigh fractionally more. It is a pretty small battery, so even a large weight difference between materials wouldn't really make that big of a difference when the weight of the entire meter is taken into consideration.

-- Doug Broussard (vought@best.com), September 25, 2000.

The Lithium batteries PX28L are an amazing improvement from the silver oxyde batteries. I do not use a spot meter but I do use them in a Pentax 67 and Bronica GS1, on both for the metering system and they work fine. They last considerably longer and keep working in the cold when silver batteries would have frozen long ago. As for if they produce different voltage, frankly, I don't know. Both are given for 6 Volts.

-- Paul Schilliger (pschilliger@smile.ch), September 25, 2000.

The Pentax Digital Spot does not appear to have voltage regulation. It instead seems to rely on the flat discharge curve of a silver PX-28 for consistent performance. I've previously used lithiums in mine, and, since they decline in voltage with use, noticed a 1/3 stop difference in readings near the end of battery life. The meter reads 1/3 stop higher with a low battery than with a fresh one. Silver cells hang on to the end, then drop precipitously. I now use only silver in the meter, and keep a spare with me at all times. Replacing the battery once a year has precluded ever having to install the spare.

-- Sal Santamaura (bc_hill@qwestinternet.net), September 25, 2000.

My experience with Lithium cells and batteries is that they are far more consistent over a given time period than Silver Oxide cells.
Lithiums have a shelf life of around 5 years, and in low drain usage, like a light meter, that equates to a usable life of several years also. The voltage drops from slightly over 3v to about 2.8v over the usable life, and even if the meter reading dropped in proportion, that would still only be a 10% error. Nothing to worry about.
There's also far less likelihood of damage to the instrument through chemical leakage from the Lithium construction.
Silver Oxides will last maybe 2 years at the most, and can, and do, leak electrolyte.
Alkalines are a definite no, no. They don't last 5 minutes (a slight exaggeration maybe), and the electrolyte is extremely corrosive if they leak.

-- Pete Andrews (p.l.andrews@bham.ac.uk), September 26, 2000.

Interesting about the alkalines, my Pentax meter came with a Sony brand Alkaline battery in the box.

-- Richard Ross (ross@hrl.com), September 26, 2000.

I checked last evening, after reading Pete's post. My P67, purchased new exactly 2 years ago, also came with a Sony Alkaline. I've been meaning to install a new silver cell in there for some months now, but, since the LED still illuminates brightly when its test button is depressed, and the RRS plate must be removed to access the battery compartment, have procrastinated. Inspection reveals not the slightest hint of leakage, not even a film on the contacts that one can occasionally see as an early warning sign of problems. I'll still be putting in a silver version soon, though; thanks for the reminder, Pete!

-- Sal Santamaura (bc_hill@qwestinternet.net), September 27, 2000.

ALWAYS carry a spare for your p67. The battery test light did not predict the demise of the orginal battery. So there I was with the mirror half way up, thirty miles from the nearest battery store. BTW, you can get the batteries at Home Depot,CVS,etc for about $2 less than a camera store.

-- Gene Crumpler (nikonguy@worldnet.att.net), September 28, 2000.

Good information Gene; thanks. Considering its extremely long shelf life, a lithium PX-28 could be the perfect spare to keep in a corner of one's P67 system case.

-- Sal Santamaura (bc_hill@qwestinternet.net), September 28, 2000.

This question was asked again on December 07, 2001, so see http://hv.greenspun.com/bboard/q-and-a-fetch-msg.tcl?msg_id=007ImE for some more responses.

-- Michael Briggs (MichaelBriggs@Earthlink.net), December 09, 2001.