Why won’t it play by battery

@phil25922 check the battery connector for corrosion and check the wires to ensure those are still attached to the battery connector. Try to power it on with a proper voltage AC adapter. If that works you know it will be strictly isolated to the battery circuit. If it doesn't work at all, check fuse F401 on the main board.

To work on it I suggest that you look at the SM posted under Documents on this site Sony CD Walkman D-NF430 If you run into any issues with that, post some good pictures of your battery connector, main board etc. That way we can see what you see and hopefully get your Walkman working again.

Adding images to an existing question