[Bob 256]

I recently purchased a K-01 camera on ebay to be converted to full spectrum which went well.

I was swapping out the battery with a fully charged D-Li90 (which I also use for my K-1) and happened to notice that the K-01 battery (that came with the camera) has four contacts as does the charger and the camera.

Regular Pentax D-Li90s have three contacts as do the Watson batteries which work in both cameras fine (as far as I know). My K-1 charger has three contacts.

I guess my question is, are the three and four terminal batteries interchangeable? Can I charge a three terminal battery in the four terminal charger?

Thanks

[Adam]

I recently purchased a K-01 camera on ebay to be converted to full spectrum which went well.

I was swapping out the battery with a fully charged D-Li90 (which I also use for my K-1) and happened to notice that the K-01 battery (that came with the camera) has four contacts as does the charger and the camera.

Regular Pentax D-Li90s have three contacts as do the Watson batteries which work in both cameras fine (as far as I know). My K-1 charger has three contacts.

I guess my question is, are the three and four terminal batteries interchangeable? Can I charge a three terminal battery in the four terminal charger?

Thanks

Yes they are interchangeable AFAIK, the 4th contact was added for health & safety reasons and is present on the D-Li90(E), which is the current battery being made for new cameras.

[clickclick]

Yes they are interchangeable AFAIK, the 4th contact was added for health & safety reasons and is present on the D-Li90(E), which is the current battery being made for new cameras.

Any idea of the specifics of those reasons? Wondering if there are do's/dont's to be aware of with the 3 contact versions. Temperature monitoring while charging?

[Adam]

Any idea of the specifics of those reasons? Wondering if there are do's/dont's to be aware of with the 3 contact versions. Temperature monitoring while charging?

I'm not sure about the specifics of the Pentax battery, but the 4th contact could be a temperature sensor to cut the current if there's a malfunction. I believe it's only used by the charger.

Adam
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[shardulm]

They are actually clearly marked inside the small circle on the Pentax branded and non branded batteries I have.
"+", "T", "-" are shown for me.
The 4th pin is more of a plastic placeholder/dummy and not a metal or contact pin. So the 4th pin if present could indicate the battery size I am thinking or a second negative "-" that catered to the older designs which required a second negative return for some oddly placed circuits.

[Bob 256]

They are actually clearly marked inside the small circle on the Pentax branded and non branded batteries I have.
"+", "T", "-" are shown for me.
The 4th pin is more of a plastic placeholder/dummy and not a metal or contact pin. So the 4th pin if present could indicate the battery size I am thinking or a second negative "-" that catered to the older designs which required a second negative return for some oddly placed circuits.

That's the case with the newer batteries (the K-1 Pentax battery and the Watson subs). The one that came with the K-01 had the fourth pin but I wouldn't think it was a second negative because it's addressed by the charger (which also came with the K-01). If it was just a second negative, the charger wouldn't need a connection to it. Also (see below), there is no voltage on it relative to the positive pin. As you mentioned, the center pin in the 3 pin versions has a T labeled on it. The battery with the 4th terminal has a label of D on it.

Interestingly, Voltage can be measured from the T pin to the positive terminal (but not the negative) and is about 0.01 volts less that + to -. It could possibly be a connection to a current monitoring resistor on the negative battery return.

Measurements between the D pin and either the + or - pin, behave like a capacitor is involved. A voltage can initially be measured but decays to zero in a short time as would happen when a capacitor charges.

One of these days when my battery gives up, I'm going to take a look inside and see what circuit is used. So far however, I haven't seen a problem using either the 4 pin or the 3 pin batteries in my K-01. I would assume it will work in my K-1 since the K-1 makes no connection to the D terminal and uses only the + and - connections which are the same in 3 or 4 pin batteries. For now, I'll charge the batteries in their respective chargers so as not to run afoul with any charge limiting differences in the two charger types.

[rmalbers]

Interesting, stuff, never really paid much attention to it. FWIW: My K50 has a four terminal battery and the charger has four terminals but the camera only uses three so that 'D' terminal must have something to do with charging, as someone has suggested.