Berlingo electrical issues

Sounds like undervoltage alright. When you say 'seems low', how low are we talking? Have you had the battery tested, or checked the voltage while the engine is running to see if the alternator is charging it properly? Could also be a voltage regulator problem. If your alternator isn't putting out enough juice, that could explain the weak battery and system failures.

Thanks for the quick reply! When the engine is off, the battery voltage reads about 11.8V. When the engine is running, it only goes up to about 12.5V. I haven't had the battery load tested, but those numbers don't seem right to me... Where would I find the voltage regulator to check that? Is that usually part of the alternator?

Okay, those voltages are definitely too low. A healthy battery should be around 12.6V when off, and the charging voltage should be 13.5-14.5V when the engine's running. The voltage regulator is usually integrated with the alternator in modern cars. Best bet is to get the entire charging system checked out at a workshop. Could be the alternator itself, or the battery is just completely shot after all these years. Don't want to be stuck somewhere!

I appreciate the advice. Took it to a workshop as you suggested. Turns out the battery was heavily discharged and pretty much defective. Had it replaced and they confirmed the alternator was working fine. Cost me 290€ all in. At least it's sorted now!