Man, i remember my first week with the fp... honestly thought i was gonna drop it and cry within an hour. I was shooting a festival back in the day and my hand cramped so bad i nearly gave up. The fp is basically a high-tech soap bar until you dress it up properly. In my experience, you have to treat it like a modular project. Over the years I've tried a bunch of different setups, but for street photography in a place like Tokyo, you want to keep it somewhat lean while fixing those hand cramps. Here is what i found actually works after testing way too many parts:

• First thing, get the SmallRig Camera Cage for Sigma fp series 2267. It is a total game changer for ergonomics. It adds just enough height so your pinky actually has a place to rest, and the texture makes it way easier to hold. It basically turns the camera from a tiny box into a real tool.
• If you hate the cage look, at least get the Sigma HG-21 Large Hand Grip. I used this for a month and it fixes the slippery issue instantly without adding too much bulk to the side.
• For the power issue, there is no magic fix other than carrying spares. I never leave the house without at least four Sigma BP-51 Li-ion Battery in my bag. They are small, so they fit in a pocket easily. Dont trust the battery meter, it lies.
• Lastly, grab a Peak Design Cuff Camera Wrist Strap. Since the body is so small, a neck strap feels like overkill, but the Cuff gives you that security so you wont drop your investment on a Tokyo sidewalk. Spend the rest of your 400 bucks on good walking shoes, because you are gonna need them.

Checking back. Are you using heavy glass? I'm satisfied with the Sigma HG-11 Hand Grip for portability, whereas the SmallRig 2671 Base Plate offers better pinky support and stability.

The out of the box experience is honestly kinda trash for the price. I was so let down by the ergonomics at first... it's just a slippery metal box. I had issues with the handling until I grabbed the Haoge THB-FPB Metal Thumb Grip for Sigma fp. Honestly, a thumb rest is way more important than a front grip for street photography because it gives your hand a real anchor point so your pinky doesn't matter as much. Regarding the power... yeah, it's not as good as expected. Its unfortunate but you just gotta buy a bunch of Sigma BP-51 Li-Ion Battery and keep them in your pocket. I usually go through three or four on a long day of shooting. Also, grab the Nitecore USN3 Pro Dual Slot USB QC Charger so you can charge your spares from a power bank while you're walking around. Without that, you're gonna be staring at a dead screen half the time. It's a shame we have to basically finish the camera ourselves, but these fixes make it actually reliable.

Like someone mentioned, the thumb grip is a common fix, but I'm actually much more satisfied with a baseplate extension for long shooting days. I politely disagree that the thumb grip is the priority here because it doesn't actually solve the pinky-dangle issue or the vertical balance when you're using a decent lens. If you're walking around Tokyo for 8 hours, you need that bottom support to prevent the hand cramps you're talking about. Here is what works well for my setup and keeps the weight down:

• Tilta Sigma fp Baseplate - adds exactly enough height for a full grip without the bulk of a full cage. It's surprisingly light and has a built-in Arca-Swiss mount.
• Panasonic DMW-BLC12 Battery - these are technically the same spec as the Sigma BP-51 but I've found the discharge rate is slightly more predictable when shooting in high-bitrate modes.
• SmallRig 2093 Wooden Side Handle - wood gives a much better friction coefficient than the slippery metal body, especially if your hands get a bit sweaty. Basically, the fp is a modular beast. Since you have 400 left, you can easily grab three or four of those Panasonic batteries and the plate. It makes the ergonomics feel way more like a premium rangefinder and less like a slippery smartphone. You'll be happy you have the extra juice too, because that 1200mAh capacity goes fast when the sensor is working that hard.

Did this last week, worked perfectly