When I purchased my WM-D6C off eBay, it was for a considerably low price, so much so that I was a bit skeptical. However it arrived safe and sound. I believe the reason it was such a low price was because it was sold without a battery pack (and that was listed in the eBay ad, so no surprises.) However that meant I had to get a battery pack. Quickly searching on eBay only showed me a few results, and they were all equally expensive (~75-100 €). However one of them was different, it was a modded pack for Li-Ion cells with a built-in charge/discharge control circuitry that can be charged via USB. Intrigued, I decided to buy it. If I was spending that kind of money on a battery pack, it better be a type that uses the most modern type of batteries. I thought the seller was making these and selling them, but to my surprise, after my sale, it disappeared from his store. Their other items are not too related, and so I think maybe the seller didn't make this mod after all. So now I have this one-of-a-kind battery pack made by some very clever person, and I have no idea where it came from! It does indeed work excellently. The control circuit is this exact model, however the dimensions are slightly off and so I believe that whoever made the mod had to cut some non-critical parts of the board off to make it fit. There is a bottom lid that was clearly 3D-printed. It also has a built-in power switch so you can prevent the batteries from draining when not in use. The control circuit has over- and under-charge protection, and it will shut off power output once the Li-Ion cells go too low. The cells are US14500UR2 (which funnily enough are made by Sony), and they're about the same size as a AA battery, which makes them fit perfectly. It has outputs in 3.3V and 5V, and the latter is used to supply power to the connection leads. To the Walkman, a 5V supply looks like a Ni-MH battery pack at ~50% charge, so it works fine. But since the board regulates the power output to be constant, it means the battery monitor in the walkman always shows the same "level" and once the batteries get too low, power is cut abruptly. If anyone has any idea of who could have made this, I'd love to know more! Also, this sounds like a fairly straightforward mod to do, so if you have a broken or spare BP-23 unit, it might be worth pulling the soldering iron and the hot glue gun out. Here are some photos of this unit: Top Side: Bottom Side (with power switch): Top side with batteries removed: Bottom side with 3D-printed lid removed (I did fumble around this a bit, this is why part of the hot clue is cut off): The micro-USB charging port:
Very interesting. I do like mods like these, if they make things better... It looks nice and easy to charge the pack with a micro USB charger but other than that I'm not sure it offers any benefit over a simple 4 x AA battery pack. These Li-Ions are only 680mAh. I guess the regulator may be 85-90% efficient at best so the actual capacity will be pretty low compared with 4 x AA Ni-MH 2400mA batteries. How long does the battery pack last?
These cells are rated at 720mAh, but are labeled 680mAh, so I'm inclined to believe that 680mAh is close to the real rating. I haven't done any accurate measurements yet, but I was once able to record to 5 sides of 90 minute tapes (2 full 90 minute tapes, and half another one), and it went out while recording the other side of the third tape, so something around ~4.2h. But I also played back some of it in between recording, so it's likely a bit more than that. One thing to consider is that the control circuit squeezes every little bit of charge as possible (within safety) from the Li-Ion cells. So while Ni-MH cells theoretically have a higher capacity, their voltage will drop considerably after a while, while this will deliver solid 5V out regardless of the charge level. I also have a second set of cells so I can quickly switch between them just like one would with AA batteries. I intend to do a full test from fully charged to cut-off to see how long it actually lasts on playback.
Very nice indeed! It would be a replacement to consider if 3 cells could be used, while fitting the electronics including the charging port in the remaining space. Although I have 2 sets of 4 Eneloops (Pro, 2400-2500 mAh a piece) that can be quick charged, which altogether are most likely a cheaper solution - not as neat though.
This would be perfect if a bespoke control circuit could be made. This one is large but relatively cheap. You can see the board is relatively empty, and all components are on one side. If both sides were used I'm sure someone could design it to be the size of a AA cell. I might do a quote on a PCB manufacturer to see how much that would cost.
Great! The market is perhaps not the biggest l, but certainly interesting. Another thought: having the USB port facing up (on top) would allow you to charge the device while using it.
Ok so quick update. I did a full run from fully-charged to cut off, playback only, with a mix of metal and chrome tapes, and the batteries lasted for approximately 6h15min. Will try again tomorrow and see if I get a similar result!
I ran the other set of batteries today and they lasted for 6h05min, which is very close to yesterday's results. I also used fast-forward and rewind a lot more today, so maybe this had an effect. In general I'm very happy with this result though, because between the two sets of batteries I can get 12h of music out of it between charges, and I could always get more batteries and a spare Li-ion charger if this became a daily carry (for some reason =P)
