I am not sure if you still need the answer. I use the Toshiba Gigibeat F40 battery. They are the same size. Just need to solder the two wires to the original battery connector.

Use two flat head screw driver. One on left and one on the right and Slowly take it out.

If you got the 410-CA, it will work. It's just the motor a little bit shorter.

For D303, if you put the discman vertically and it plays fine, the motor needs to be replaced.

I personally found many Portable players decode WAV better than other lossless files like flac, ape.  I am not sure why but same song will sound the same with foobar when I play it with computer or laptop in any lossless format.  So weird.

I found this Sony MDR-225G earbuds from ebay for only $29.95. They are cheap and look cheap but have huge sound stage and great sound quality (Better than E888). These are earphones from 80s.  Unbelievable that they still available!

I don't have D311 to compare.   But this thread is a great resource for Discman review.   http://www.head-fi.org/t/31233/personal-cd-players-through-the-ages-a-review-updated-10-05-2003   Quote:

Still love the sound of my D35, D303, D321.  Best sounding ever!

why not buy a new hand unit?   Quote:

Anyway to have something that can fit inside the battery compartment?  It would be much better for portable use.   Quote:

Brand--SanDisk Speed Class--4 Size-- 32GB Compatible-- Yes Firmware Version/Date--V0.19 http://www.newegg.com/Product/Product.aspx?Item=9SIA12K0C43228

nice collection.

I was just playing some 16/44kHz wav files.

rockbox my hm801 but immediately feel like degrade on sound quality.   also i notice that the player was cooler when running Rockbox.

Hifiman series