Same voltage. But the EN-EL3a has the same voltage and the same 1500mAh capacity. The "e" version may add power monitoring circuits (ala Sony's infolithium). Perhaps there are extra contacts. We likely need to see a manual to know if other cells are usable.
It would be a poor move on Nikon's part to make a new battery with the same form factor as earlier cells and not have them be compatible. If you had a mix of batteries in your camera bag it would be an extra hassle to avoid inserting the wrong cell, not to mention the extra cost if you have to buy more e-version batteries.
To say nothing about not being happy about investing in several EN-EL3a batteries already and then not having them usable anymore! I think it would be short-sighted of them (but I wouldn't be shocked).
One reviewer speculated that the EN-EL3a might work, but that some of the new detailed features like the number of shots since the last battery charge and the % of battery charge left might not work with the older battery. If he is correct, I could live with that compromise.
"Climb the mountains and get their good tidings. Nature's peace will flow into you as sunshine flows into trees." John Muir
The photo I saw of the new battery shows a third contact bewteen the normal two. I believe this exists to allow internal battery measurements to be made available to the camera in order to give a more accurate display of the amount of battery life remaining.
If that's the case, it would seem simple for Nikon to have designed the D200 to run from older EN-EL3 batteries but disable the additional battery percentage indication when a non-EL-EN3e battery is in place. Let's hope that's what they did.
According to dpreview, the manual specifically states that the older batteries are NOT compatible. Thats not to say that they won't work, it just means that they won't work with the new battery monitoring capabilites of the D200. Of course, I'm not sure I'd want to take the chance of screwing something up electronically by using the wrong batteries.
if you ask me, the form factor is PROOF that the old EN-EL3 and EN-EL3a's will work to some extent. one of the first things you learn in engineering is that directions and warning labels are not nearly enough. if you don't want a user to do something, you have to make it such that they CAN'T do it. cuz users WILL do it otherwise. this is what they do with power cords. in the appliances that matter, you can only plug them in one way and not the reverse. if they didn't do this, there'd be a lot of fried appliances and a lot more burnt down buildings. anyways, i'm as sure about this as i am sure that the nikon engineers are not stupid. besides, if nikon is trying to keep as many users as it can, and hoping d50/d70/d100 users will upgrade, this only makes sense. my guess is that the only 'non-compatible' things are the 'fuel gauge' features.
I'm with you. It's a simple enough thing to come out with a new EN-EL variant that makes it clear the battery is unique. Nikon's smart enough to do this right. I bet that we'll find that the "e" battery is required for the monitoring accuracy. It's possible that the other cells would be monitored less accurately or not at all, hence the "incompatible" designation.
The MB-D200 grip is supposed to work even with six AA cells, so it DEFINITELY will work with a couple of EN-EL3 or EN-EL3a, without monitoring. As fro the body itself, I hope the situation is the same.
I've got 4 of the older batteries and it would be really bad if they "fit" into the D200 but the camera would not start up or worse cause a problem. I have no problem with the old batteries not supporting the new battery functions that the D200 offers. But they should at least perform the basic camera operation. Otherwise, they should have come up with a new model name and form size. I think that the old batteries will turn out to work for everything except for the new D200 battery information.
I can't see Nikon making a battery with such a close model number that it wouldn't work. I think all the EN-EL3 versions will work but the earlier ones won't provide battery level information. Similarly the CP8400 now has an 'e' version of it's standard EN-EL7. The e version has a fuel gauge but the camera wasn't originally designed to read the additional info - unlike the D200 - but it still works. I suspect all new batteries will be the EN-EL*e type for new cameras and backward/forward compatable.
My mother once had a Ericsson cell phone which also had a battery life prediction, but only for Ericsson batteries. We bought a no name replacement battery when it died, at 50% of the price. Guess what? Only had two contacts instead of three but worked fine, without predictions.
I guess this will be the same. The camera must have some protection to work with new batteries of which the monitoring fails, so probably old batteries will work.