Lost voltmeter

After a tip from Informant, you meet Winsor, the engineer who haven't found his place on Big Land but has his skills in high demand in the Zone. Winsor says he invented a device that lets you recharge batteries from the energy stored in artifacts, and can give it to you for a price.
You have to find and return his voltmeter he left in the railway tunnel at Darkscape when he was running from Graystone mercenaries who arrived into the zone during Arc of Fire.
==Walkthrough==
The quest starts with Informant's dialogue about a charging device, available after completing Combat. After this dialogue, Winsor spawns at Construction Site in the [ power substation] at southeast of the location. Go and speak to him.
The voltmeter is located in the western end of the [ broken bridge tunnel] in an extreme radiation hotspot. The exact location is shown on the video below (0:55).
You will likely be maxed out on radiation before grabbing it since it's necessary to crouch to reach the toolbox stash it's in. For this reason, it may be worthwhile to hotkey anti-radiation drugs for the coming fight.
A squad of mercenaries will spawn on the broken bridge and at the [ workshop]; one of them will be carrying a VSSK "Vykhlop" and three in green modernized exoskeletons will be wielding RPG-7s. They will continue firing missiles at you until killed, however they do not seem to aim at your feet so you can dodge these if you aren't standing near a wall. A few underbarrel grenades or a long Vortex grenade throw will also be a good option to quickly clear out the initial attackers while looking out for one mercenary ambushing you from the workshop door on the left. The rest of the mercenaries should not be too difficult to pick off.
Turn in the voltmeter to Winsor for coordinates to a stash in the Dark Valley that has the Portable battery charger, allowing you to recharge exo batteries in the field.
==Notes==
* It's normally not possible for the player to traverse up to the tunnel from below the tracks on the west side of the tunnel, but this doesn't stop the mercenaries from going up and down the sides of the tunnel.
* Winsor has his own faction, "Dark".
==Bugs==