Interestingly, the sleeker looking SJ-MR240 (MDLP, no NetMD) and SJ-MR270 (MDLP, NetMD) came out at nearly the same time, but look much more modern and used a different dock (same speakers).
Often, these show up without the dock or in an unconfirmed state because of power issues. I have a few of these, and it typically is the hinge at the battery door causing problems. The hinge is crimped/clamped into place and after years of use, it can get loose, making poor contact. We can test this by jamming some copper in there to help the electrical connectivity. Once we confirm it, we'll want to fix it more permanently and that's where some thin copper sheeting (cut to fit) can come into play.
In this video, you'll see a bit of troubleshooting to confirm the issue, then fixing it with a thin piece of copper cut from a roll. I used 0.1mm thick copper, but I'm sure you could go a bit thicker. I've also seen some people remove most of the original battery door contact and replace it with a strip of brass or nickel.
For the copper listed in the video, I used:
Copper sheet roll 1000mm x 100mm x 0.1mm
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Chapter markers
00:00 - beginning
00:28 - "no battery"
1:19 - examining the battery door
1:38 - test copper in the battery door hinge
2:10 - closer look at the hinge
2:59 - disassembly - bottom case
3:41 - a bit of cleaning...
5:20 - testing with a longer piece of copper foil
6:28 - reassembly - bottom case
8:16 - setting up the dock and speakers
9:45 - copper piece from a roll of thin copper
11:54 - testing
12:40 - take the battery door cover off
16:02 - bend the copper over the "finger" on the battery door contact
17:50 - image - soldered in place from the rear and near hinge