Thanks to ch_cannon's post on using film I dragged... (
I am not certain what the F2 uses.... I see some posts online that mention using two 1.5 volt SR44. Those (or similar 303 or 357, depending upon the manufacturer) are Silver Oxide batteries which perform very similarly to the now unavailable mercury cells that were original to many cameras of that vintage. If the F2 originally used 675 size mercury, SR44/303/357 are almost exactly the same size and should fit fine. If the camera originally used the larger diameter 625/PX13 mercury, see below how to adapt the SR44 for use in Gossen Luna Pro. With the modern batteries you may need to "tweak" your ISO/ASA setting slightly if the camera was originally designed for 1.33 volt mercury... but some cameras have a voltage regulator built in, in which case the slightly higher 1.5 volts of the silver oxides won't make any difference. It might be possible to have the camera's meter re-calibrated to the new batteries... some have enough adjustment built-in, while others require a diode or something added to the power circuit.
Of course, you could use the camera without any battery. The F2 is purely mechanical, not battery dependent and you can make your exposure settings using "sunny 16", etc. or using a separate light meter. (Other Nikon this isn't possible... If I recall correctly FM2N, FE2, FG and some others with electronically-controlled shutters require a battery.)
As to the Gossen Luna Pro, they originally used 625 or PX13 mercury cells and I don't believe have a built in voltage regulator. Those no longer available batteries are larger diameter than the replacements, so Gossen themselves made an adapter that allows a pair of the smaller SR44 to be used in the meters. I'm fairly certain the Gossen adapter also corrects the voltage to a proper level for the meter. The Gossen "GO 4145 kit" includes both the adapter and a pair of SR44 batteries. HOWEVER, it's hard to find now. AFAIK, it's no longer being made. If you search long and hard for it, you might find it... maybe just a the adapter used from some source. The kit was rather expensive initially (about $40 last time I saw one), but that's a one-time purchase of the adapter and you can find replacement SR44/303/357 batteries almost anywhere for relatively little money. (Note: This adapter also can be used in some cameras that were originally designed to use a stacked pair of 625/PX13 mercury cells... it's a tight fit in some camera battery compartments, but the outer shell is made of hard plastic and can be sanded to reduce its diameter and make it fit.)
Failing to find the Gossen GO 4145 kit, it also is possible to buy "generic" adapters that allow the smaller SR44/303/357 to be fitted to other cameras. I've bought them for various cameras. They are simply machined out of brass and mostly serve to "take up the extra space" in the battery compartment, due to the smaller diameter of the modern batteries. H
OWEVER, I've also used simple 20 cent, rubber o-rings bought from local hardware stores, to serve the same purpose. Those work fine when only a single battery is used, or with stacks of batteries, so long as the negative contact isn't on the side of the battery (which would be insulated by the rubber o-ring... Canonet QL17 GIII uses a side-contact battery arrangement).
If you want to try this, buy a couple SR44/etc. and take them and the meter to a hardware store with a selection of o-rings, then find a size that will fit on the battery snugly as well as make for a proper fit inside the meter's battery compartment.
There are also "hearing aid" 675 Zinc Air batteries that are the same dimensions and can work in place of the silver oxide, similarly shimmed to fit the battery compartment. Zinc air do not have nearly as long a life as silver oxide, though. In cameras and meters they typically only last a month or two. And, once you unseal zinc air to activate them, there's no stopping the process. They will go dead in a month or two anyway. (With silver oxide, which can last about a year, they stop draining when removed from the camera.) 675 hearing aid batteries are cheap.... usually sold in packs of 10 or more for a few dollars. I buy and use them for short-term testing of old camera gear, in place of the more expensive but longer lived SR44/etc.
I don't think it's the case with the F2 or Gossen Luna Pro, but some cameras were designed to use four stacked 675 size batteries.... in those it's possible to either use four SR44 or a 4SR44, which is a pre-made "stack" of four of those batteries.
There are also "Varta" batteries (and other brands which are similar) sold especially for photographic uses, which are simply zinc air 675 with a metal shim pressed on to bring them up to the same diameter as the original 625s. They may last a little longer... maybe two months of normal usage. But they sell for much more... often $5 or more each.
Zinc air batteries usually have around 1.4 volts apiece, which is closer to the original mercury batteries and makes for less skewing of metering systems that don't have a voltage stabilizer.
DO NOT use alkaline batteries. You can find them in similar sizes. But they will give incorrect readings more often than not. Later cameras designed to work with alkaline all have a voltage stabilizer because the power curve of alkalines is rather steep. They start to lose right away and continue to drop steadily. In contrast, both zinc air and silver oxide have fairly flat power curves... they maintain a level voltage for a long time, then die suddenly... much the way that the old mercury batteries did.
In some cases it's possible to re-calibrate cameras and meters to be accurate when used with the slightly higher voltage modern zinc air or silver oxide batteries (you have to commit to using one or the other and be sure any you buy have the same voltage... there is some variation). If that were done with alkaline, it would only be correct briefly during the life of the battery... and out of calibration the rest of the time.
But it's also often possible to simply "fudge" your ISO settings a bit to compensate. I've found that zinc air, which are usually about 1.4V (2.8V for a stacked pair) and only slightly higher voltage than the 1.3V to 1.33V mercury (2.6V to 2.66V pair).... make for approx. 1/3 to 1/2 stop skew. The usually 1.5V (3V) to 1.65V (3.3V) silver oxide batteries may cause a full stop of skew. HOWEVER all this assumes the old metering system is still accurately calibrated for the original batteries. There's good chance it's slightly out of adjustment after all these years (which may or may not favor the modern batteries), so you pretty much have to test and evaluate each camera or meter with your choice of battery and tailor any adjustments or re-calibration accordingly.
Another minor thing.... When you first install silver oxide batteries, they're often slightly over-powered. Look for them to "settle down" after a half hour or so. Conversely, when they are first unsealed zinc air batteries are under-powered... they come up to power in 15 minutes to half an hour. So in both cases it's best to not fully trust meter readings for a half hour or so after installing a fresh battery.
If you find them in sizes that might work, generally DON'T USE lithium or Nicad batteries in the cameras and meters originally designed to use mercury cells. They might damage those cameras. (OTOH, some cameras, such as Canon A-1 and AE-1 are able to work fine with silver oxide, alkaline or even lithium batteries... no problem. Just don't "risk it" with other cameras, unless you know for certain they are okay to use.)
Finally, another reason to NOT use alkaline is that they seem to be the most prone to leaking and damaging cameras (the original mercury could leak, too). Zinc air are probably the safest and least likely to leak and do damage. Silver oxide are pretty safe, too.
EDIT: I notice someone else mentioned the CRIS MR-9 adapter, which is another solution for anything that originally used a 625/PX13 mercury cell. https://shop.criscam.com/products/mr-9-mercury-battery-adapter
I forgot about those! The MR-9 is pricey at $36 per battery (and I'm cheap... so bought 20 cent rubber o-rings instead), BUT it has built in voltage correction to allow SR44/303/357 silver oxide to be used without need to re-calibrate the meter (assuming it's not out of adjustment anyway). This may make a lot of sense when only a single battery is needed. If I recall correctly, all Luna Pro use two batteries... So you'd have a one-time cost of $72 for two of those adapters, and then the on-going cost of fresh SR44/etc. every year or two after that.