Finding atomic battery locations in is one of the key progressions in the game, as you power up the quarantined facilities of the Interchange and open the way to Oberon. These nuclear power sources are quite rare and there are only a limited number scattered around the map, generally at the end of enemy-infested areas.
You can also bargain for atomic batteries with some traders or even fight giant robots for them if you'd prefer to take the nuclear option, so to speak. Here's where to find every atomic battery I've located in Atomfall. Considering you only need a fraction of them to power up the Interchange, you've got plenty of options.
Buy three of them from traders
You can barter for an atomic battery with three different traders in Atomfall. The first is Molly at the Trader Camp is Slatten Dale, just to the west along the road from the Wyndham Village entrance. Her coordinates are 26.4E, 79.1N. Molly likes molotovs, so bring some of those to trade if you have them.
The second trader to sell one is Nora at Nora's Barn in north Skethermoor. This is directly east of where you enter the region from the village and Brinsop Manor. Her coordinates are 41.8E, 77.5N. I'm not sure what Nora likes so try experimenting with different items for a bargain.
The final vendor is Billy Gorse at the Trader Camp in northwest Casterfell Woods. His coordinates are 21.5E, 89.9N, just to the south of Casterfell Dam. Billy likes Burn Salve for some strange reason, so trade that if you have any.
Open Vicar McHenry's chest
While I'm not talking about opening the Vicar's literal chest cavity—he ain't Iron Man—Vicar McHenry does have an atomic battery stashed in a chest on the upper level of St. Katherine's church in [[link]] Wyndham Village. If you're feeling charitable, you could help him with the problem, and he'll give you it as a reward. If not, you can always just blast him and take his key. God will understand… probably.
Salvage two from wrecked robots
While bartering with Nora at Nora's Barn in Skethermoor, be sure to investigate the pond behind her house. At its centre you'll spot a sparking robot with an unclaimed atomic battery. Bad news, though—this pond is filled with ravenous leeches and their biting you will stun you out of the action to claim it. I suggest going to the far side of the pond—which is closer to the robot—and then jumping in and doing it as fast as you. This should give you ample time before the fish try to feed.
There's also a second wrecked robot with an atomic battery in Wyndham Village, at coordinates 34.4.E, 80.7N, slumped over a wall by the Village Green. I'm not if this is there when you first enter Wyndham Village, since it might appear later as you progress.
Kill robots
Hey, you know those robots you see wandering around? They've got atomic batteries in them, they do. Beat any robot in a fight—ideally using grenades—and they will start to overheat. If you run behind them and claim their atomic battery while they're crouched down, they'll shut off, and to add to the bargain you'll get a fancy new atomic battery.
Find one in the Interchange
When you first enter the Interchange, you'll find an atomic battery in the central processor by the corpse of a scientist. Of course, you'll need a battery to plug into the processor to activate the facility, so it's kind of a moot point, but hey, at least it's a free one you didn't have to find.
Find one in the Castle Ruins
There's an atomic battery located in the Castle Ruins—the druidic stronghold in the southwest of Casterfell Woods. Honestly, the druids are a pain since there are tonnes of them and you'll have to do a whole lot of killing to get close the first time you visit. Rather than the main castle entrance, you'll want to head east and look for a smaller door that's just down a long ladder by a druid totem.
Once inside this cave, navigate to the centre of the area and the giant pit filled with blue fungus, where the druids are chucking anything vaguely technological. On one side of the pit you'll spot a staircase, and at the top of it on a little overlook, you'll find your atomic battery.
Find one at Casterfell Dam
You can find this atomic battery near a power generator at Casterfell Dam in northwest Casterfell Woods, coordinates 20.9E, 90.9N. Look for the sparking generator cages and inside the most north-easterly one, you'll spot a skeleton with a backpack and an atomic battery lying nearby.
If you don't want to get zapped you need to head past the generator cages to the control room and use the Substation Override lever to switch the power—you want the top light on the map in the control room to be red. When that's done you can safely enter the cage and grab your battery.
Find one in the Vehicle Storage Bunker
This last atomic battery is in the Vehicle Storage Bunker in east Skethermoor at coordinates 43.4E, 74.6N. This facility is infested with outlaws that you'll need to deal with, but after that you can find the atomic battery in the facility storeroom after exploring a bit. This storeroom is filled with bad batteries releasing radiation, so [[link]] you'll want to take some radiation resistance medicine so you don't die.
If you don't have the recipe to craft it or any to hand, you can find a copy of the recipe in the same bunker by a corpse leaning against a workbench. Take your medicine and then run through the storeroom to grab the battery at the far end.