I recently bought two of these emergency fixtures with a 8 watt T5 tube inside it. I removed the battery because I don't need it for my intended purpose. But I can't find any information about how these actually work. The coil on the right seems to be a transformer, in the middle a small coil you also see in modern switched power supply's and at the left another coil from the same size as the right one. Is this a simple choke ballast? When running on 230 VAC mains power the lamp is not running on high frequency as is seen through a mobile phone screen. Before I take the PCB off and breaking the plastic pins holding it, can anyone shortly explain how this thing actually works? It also doesn't have a starter switch.

By the looks of it, the ballast inside this fixture is a special electronic emergency ballast and not a simple inductive series choke ballast.

In the gear circuit there is an inverter to convert 230V AC to low voltage DC, which is used to charge the battery and run the lamp. The running gear is a low voltage instant strike circuit ballast, similar to caravan fluro lights.

There are two categories of emergency light in the UK: Mintained, and Non-maintained. Maintained fittings will light up as soon as the mains is connected (most allow the lamp to be on a switch without cutting power to the battery charger). Non-maintained fittings will only light up if the mains supply is disconnected.

It indeed behaves like an instant start ballast. With the battery, which i already removed it is a maintained fixture.  But instant start is not really what I like so I might do a preheat conversion or even a warm start electronic ballast conversion. I also have the idea to make it some sort of 18 watt sox fixture

But that makes things way more difficult and I have an almost infinite supply of 8 watt T5 lamps.

But maybe someone has other suggestions 

I see there two 50/60Hz magnetic things. For sure one of them is the transformer used to charge the batteries, the second could be either charging as well (from the second power input line) or the series inductor ballast for mains powered operation.

For the battery operation I see there a HF transformer, few HV capacitors and an inductor, tell-tale signs of a "Royer oscillator" style inverter circuit.
And a relay, most likely used to switch the lamp over from the mains to the battery ballasts.

I doubt the lamp would be powered from the mains via the low voltage circuit, that would invoke way too much losses, plus the low voltage circuit is designed to operate the lamp at very low power, too low to maintain the lamp life (it is intended to burn for just few hours per year, while anticipating about the typical 10 year service lifetime)

When operated on the battery the lamp is significally less bright for sure. I tried to desolder the two big 50 Hz components but was unsuccesful. If one of them was a regular ballast it could be useful. In the end I used a more easy solution. I removed the gear and installed a May & Christe 230V ballast. The lamp seems to shine even brighter, the mains voltage when testing was 238V. I used a Philips S2-E electronic starter.