I also done a bettery test, the battery failed the test, didnt save it but im sure it said at the bottom somewhere AC test OK. I put a volt meter, switch to 200v AC on the battery and got a 30.9 reading, does this waveform look ok ??
That ripple waveform looks normal to me. The spikes are interference from ignition or injectors and are pretty normal - wires in the loom run pretty close to each other so such spikes are a fact of life. Switch on a filter - about 10kHz and they will go away.
As for the voltmeter, some of them can not cope well with spikes so give odd readings. Best to rely on the scope
Feel free to save the battery test and post here for comment.