This sounds like some things are losing electrical power at the same time as other are getting too much. I would start by checking all the wiring and connections between the alternator and battery, including earth (ground) connections. Am I right in thinking the battery is in the boot (trunk)? Any dampness here could lead to corrosion around the terminals.
Either way you need to get this sorted quickly, excess voltage can destroy electronic components including those in the alternator itself.