Made a compact oscilloscope, portable! No idea why these models are shipped out with AC-only power options with how small they are. Nevertheless, it's just begging for a battery, so let's do it.
This is a really commonly available, affordable beginners' oscilloscope that I personally really like. Here's a link to it. It does what you need it to do, shows measurements accurately, navigates its firmware pretty speedily, and has all the basic features you need to analyze voltage signals.
So first, a list of the parts needed for this project:
-Battery. I chose to go with a 7.4V 2S 300mAh battery for this as it's a good fit for the case, and (kind of extraordinarily at first glance, since it's 7.4v and the DSO150 is calls for 9v DC) runs perfectly on the DSO, without the need for any voltage boosting or bucking circuitry to power this, meaning you really only need 2 components in this mod.
-BMS (Battery Management System) 7.4V 2S to regulate voltage while charging/discharging.
-Soldering iron. If you're here, you likely already have a soldering iron. But I'd 100% recommend the model linked as an affordable bench iron. If you want to go fully portable though in the spirit of this project, I also 100% recommend this iron (TS80P) as it's USB-C powered and extremely capable.
-5x 22gauge jumper wires (like breadboard wires)
-Knife or anything to strip and cut jumper wires to the right size
-Small Philips Screwdriver
Now on to the steps.
First, you need to disassemble the DSO of course. It's just 4 philips screws in each corner, easy as pie.
Next you pry the daughter board from the mainboard, it should only be attached by an 8-pin connector toward the top of the device.
Then, you'll need to identify the power pins we'll be working with on the mainboard. When looking at the backside of the board, toward the bottom left corner you'll see a white box with the + and - signs above 2 pins. That's where we'll be soldering. These pins run back to the same pins the AC barrel connector goes to, so you'll be able to recharge these batteries through the wall like any other portable device.
Now we'll need to look at the BMS we got, and understand how we're going to work with the 3 wires coming off the battery (ignore the big XT60 connectors if you have any, they have a yellow top and are more for hotswapping batteries in applications like RC cars. Taking a look though, this isn't too hard. The BMS has B+ and B- labeled pinholes waiting for those connections from your battery. But we've got 3 wires on our battery, the red (positive) and black (negative) are straightforward but what do we do with the blue one? Well, that should be for battery protection/thermal monitoring. And your BMS has a spot to interface with it too! Right underneath the P+ and P- pins, you should see a pad named BM. That's where you'll connect the blue wire.
The process to do it is really finicky, I don't have any solid way to walk you through how to position the wires while you solder. If you have something like this, along with some Helping Hands, that should be able to keep you a bit more steady as you solder.
Begin soldering the wires to the BMS, all 5 (B+, B-, P+, P-, and BM). This will help you gauge how long each wire will have to be so you can trim them down to size, and figure out the right positioning that works for you with the battery and BMS inside the case. I would use traditional colors just to keep track, so red for +, black for -, blue on the BM pad, to correspond with the battery's blue wire. But you can do it however you want.
After you've got solid connections and the wires are stripped and ready to solder to the board, go ahead and solder the P+ and P- wires to the + and - pins identified in step 3.
Then, you can connect the battery (strip the B+, B- and BM wire sheaths down far enough to slip into the female receptacles of the battery, matching the colors.
You can try and flip the power switch of the DSO150 now, with the AC barrel connector unplugged, and see if it boots.
If it doesn't turn on the first time, don't worry- make sure the connections are tight, connect the AC barrel connector (and make sure it's plugged into the wall), and power it on. After it hopefully boots up with the help of the AC connector, disconnect the barrel connector and the power should stay on.
Then, you can power it off and back on without the barrel connector in and it should work, no wires at all!
Power it off and go ahead and wrap the connections in electrical tape to make sure they don't short when you seal everything up.
Screw the device back together, and you have yourself a new fully portable oscilloscope!
You can charge this like anything else now, but keep an eye on it for the first hour just to make sure nothing's getting too hot or starting to smoke.