I bought a couple of DSO-150 oscilliscope's a few years back, mostly to just check capacitance on different comparator circuits that I was working with. These work pretty good. I finally got around to making them rechargeable instead of having to plug them in all the time to use them. A lot of other people have done this to the DSO-150 too so it is overdue. The process is pretty simple. The switch that I installed is DPDT center-power, low for charge mode, up for scope power. I did leave the stock switch in the unit, sort a safety measure. Im using a very cheap but nicely makde buck converter board - a note about this particular board, the selector conductors must be unsoldered first and then solder them according to the output that you desire. The markings are plainly layed out of the back of the boards. They work very well. There is ample room inside the enclosure for this modification. My only advice would be to take your time and watch your step, these batteries aren't very happy if you make a mistake.

DSO-150:

https://www.aliexpress.us/item/3256805372061422.html

(many many places)

Switches:
https://www.mouser.com/ProductDetail/123-09.03290.01

3~5/8/9/12V Buck Converter:
https://www.ebay.com/itm/254645736219

 5V Mini USB 1A TP4056 Lithium Battery Charging Board Power Charger:
 https://www.ebay.com/itm/314221153381

 Recommended:
 https://www.ebay.com/itm/264450592969

 
 3.7V 1000mAh Li Polymer Lipo Rechargeable Battery For MP3 GPS DVD:
 https://www.ebay.com/itm/112369054465