Mac Classic 0000000F and 0000000D error

Just obtained an old Mac Classic 1990/1991.

The screen seems okay; it boots to a blank white screen. However, when I press the reset/interrupt, it gives the error code:

0000000F

0000000D

I looked inside and the battery and socket were fried. I cleaned it up, but the + connector on the batter socket was snapped. I used tin foil to try and seat the batter correctly. On the underside of the motherboard, directly under the batter, some of the solder dots seem to have flattened. I've had some strange results since.

1. When I first cleaned it up, including the old battery, it eventually booted into the curved edge screen, with a mouse pointer. However, it soon crashed back, but with a different error message

0000000F

0000000D

2. I tried to wire it up to a wall charger and sent in voltage of 3 or 4 to it. What happened was the blank screen, but a couple of pip noises every 10 seconds or so.

3. I now have a new battery. I put it in using the tin foil method, but apart from the couple of pip noises, it has reverted to as before.

I've done the usual: removing memory, starting with or without hard drive or floppy connected. My next stage today is to wash the motherboard.