Yes, you want the flatter 357 batteries. Tim has posted some good info
some time ago (See Below). Some batteries are designed for watches that
have low current drain and tolerate a higher internal resistance. The
good 357's have lower internal resistance and can handle the larger
current pulses required for the shutter release. There is an internal
low voltage detect circuit in the OM-4t's that will trip and lock the
shutter open if the battery drops too low with these pulses of current.
You will note that it is more likely to happen in cold weather, where
the battery chemistry performs worse. Still, the silver oxides do a
much better job than today's lithium ion rechargeable batteries at
low temperature. No wonder the E-1 battery is in the hand grip.
Also, if you measure the current, some meters may not get the current
exactly right because it is duty-cycled (pulsed). Ever notice when the
camera has been inactive for a few minutes, you depress the shutter to
activate the meter and it will have some delay coming back on. That is
caused by the duty-cycle. I'm guessing Oly lowered the duty cycle on
the 4t to get lower current drain compared to the OM-4, but I could be
wrong.
I test my batteries on occasion, using a resistance load (5-10K ohm)
and compare it to the open circuit voltage to get an idea of the
internal resistance. The metering on the OM's may have some sensitivity
to voltage. I think the service manual recommends meter calibration
using a 3V power supply (but I depend on the experts for doing any
calibration).
\A/yne
Some Old Posts from Tim Hughes: Note particularly the very last
6 paragraphs in the 2nd post. Everready 357's are a good choice.
=============== 27 Jun 2001 ==================
Dear Omer's,
Warning lots of Engineering stuff follows.
II have been looking at various batteries to power some
new products I am developing at work. While I had Energizer/EverReady
technical staff helping me with information, I decided to find out more about
the 357 (SR44) style batteries we use in most of the OM cameras.
* The silver oxide batteries **from all manufacturers** contain something
like 0.3 to 1% mercury! This helps preserve the anode. Internationally up to
25mg of mercury per cell is considered acceptable.
* Although various battery books list that AgO cells lose capacity at up to
5% per annum, Enegizer claims their cells lose capacity at 2% pa or less at
room temperature. Sealing is now so good that tested shelf life exceeds
10years. In accelerated (high temp aging tests) the cells have even longer
projected shelf life. This would means it is hardly worth refrigerating
cells. (Normally ~doubles shelf life for every 10C reduction).
* High current pulse rated cells like the 357 all use KOH electrolyte. Low
current rated cells like the 303 use NaOH electrolyte. Vendors like Duracell
(who don't actually make their AgO cells themselves) mark their cells
357/303 and ship only the high current version. It used to be that the KOH
cells were much harder to seal as the electrolyte is more active and attacks
the seals and cell seperators. The capacity was also a little lower as the
seperator needed to be thicker. This is no longer true. Why then, does anyone
make NaOH cells anymore? The answer is watch vendors often demand a NaOH cell
as they still believe the sealing is a problem and are worried that the KOH
cells are more likely to leak and cause damage. The sealing on some vendors
cells may still be problematic, so avoid generic brand cells.
* The 357 cell is capable of short circuit currents up to a couple of hundred
mA when new and for short durations (<100mS).
* The Energizer 357 cell capacity under low rate conditions is higher than
the nominal 175mAh rated , approaching 200mAh. (The very old data book values
used to be 200mAh but this was at 35C (wrist temperature, which helps a
little.) not 21C. This helps with OM4's and 2'S's which have higher "off "
standby current. The 357 cell has been significantly reformulated over the
years since first introduced for use on LED display watches.
* It would be interesting to compare Energizer's cells to those from other
vendors. In particular an accelerated life test would be interesting and a
high rate capacity test to see if there really are differences.
Regards,
Tim Hughes
>>Hi100@xxxxxxx<<
================= 5 Aug 2002 =================
Following the perenial revival of the long dead horse topic of OM
batteries, here is an old post of mine to the OM list on batteries,
(Mark Dapoz had copied this onto his website)
I have added a bit more new information at the end, based on some more
information from vendors:
>>I have been looking at various batteries to power some new products I
am developing at work. While I had Energizer/EverReady technical staff
helping me with information, I decided to find out more about the 357
(SR44) style batteries we use in most of the OM cameras.
The silver oxide batteries from all manufacturers contain something
like 0.3 to 1% mercury! This helps preserve the anode. Internationally
up to 25mg of mercury per cell is considered acceptable.
Although various battery books list that AgO cells lose capacity at up
to 5% per annum, Energizer claims their cells lose capacity at 2% pa or
less at room temperature. Sealing is now so good that tested shelf life
exceeds 10years. In accelerated (high temp aging tests) the cells have
even longer projected shelf life. This would means it is hardly worth
refrigerating these cells. (Normally ~doubles shelf life for every 10C
reduction).
High current pulse rated cells like the 357 all use KOH electrolyte.
Low current rated cells like the 303 use NaOH electrolyte. Vendors like
Duracell (who don't actually seem to make their AgO cells themselves)
mark their cells 357/303 and ship only the high current version. It
used to be that the KOH cells were much harder to seal as the
electrolyte is more active and attacks the seals and cell separators.
The capacity was also a little lower as the separator needed to be
thicker. This is no longer true. Why then, does anyone make NaOH cells
anymore? The answer is watch vendors often demand a NaOH cell as they
still believe the sealing is a problem and are worried that the KOH
cells are more likely to leak and cause damage. The sealing on some
vendors cells could still be problematic, so avoid generic brand cells.
The 357 cell is capable of short circuit currents up to a couple of
hundred mA when new and for short durations (<100mS).
The Energizer 357 cell capacity under low rate conditions is higher
than the nominal 175mAh rated , approaching 200mAh. (The very old data
book values used to be ~200mAh but this was at 35C (wrist temperature,
which helps a little.) not 21C. This higher capacity at low rate helps
with OM4's and 2'S's which have higher "off" standby current. The 357
cell has been significantly reformulated over the years since first
introduced for use on LED display watches. <<
Some new information: A battery vendor who makes batteries aimed mostly
at the watch market told me his batteries don't last more than 4 years
and quoted me a loss of capacity of as much as 10%pa. It would definely
pay to refrigerate these cells! (Although not in the deep freeze).
A very significant issue for OM use, is the change of battery internal
resistance as the cell ages, and of course near the end of discharge
life. This causes increased battery voltage drop at peak camera
operating currents at shutter opening.
One vendor's batteries show an almost doubling of resistance after one
to two years of storage. In general the resistance increases sharply in
the last 20% of discharge life and is what ultimately causes sudden
camera lockup in OM's. The resistance change in storage appears to
depend on the vendor's process and may be the reason why certain "new
unused cells" cause lockup in the OM occasionally. The resistance in
the case of the watch vendor's cells, increases after a year or two,
and then drops off again to closer to new values after about 2 years.
Based on Everready's longevity claims (not tested myself) their 357's
do not suffer from the large increase in resistance or fail after a
some years of storage. Hence my recommendation: stick to Everready.
The battery life in OM use, is probably as much related to battery
resistance near end of discharge life, as it is to rated capacity in
mAh. It would be interesting to run some discharge-resistance curves to
compare different vendors cells.
When I asked Everready about the '76 type (SR44 size), which are shown
as having a sloping discharge voltage near end of discharge, the tech
support person said he thought they no longer had that characteristic,
although he was not completely sure! Cells with a shelf life end of
discharge curve, were engineered at one time to allow easy end of
battery life detection.
Regards,
Tim Hughes
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