Fitted a new battery due to not being used in lockdown the oe battery died. New one is correct spec Yuasa efb, no problem there, been fine for 2 months. I have charged by accumate trickle charger in situ every 2-3 weeks so this doesn't go the same way. Checked with multimeter, battery 12.5v after 2 weeks off charge, good. Started engine 14.5v dropped over 1-2mins to 12.2v? this would normally be 15v & hold steady, checked 2 weeks ago. Switch off & try again, same thing 14v dropped to 12.2v. Switched everything on inc aircon & it reads 13.5v? Switch aircon off drops back to 12.2v. Seems like the alternator is charging at high demand, but not low. Fitted a voltmeter in cig socket & went for a run to check, every so often it would go up to 13-14v then drop back to 12.2v.

Anybody had similar, got any clues to the problem? TIA for answers.

Paul

Did you reset the battery monitoring system after fitting the new battery? The smart charge system will be trying to maintain the battery at about 80% charge, if it's already at 100% charge the system doesn't want to waste fuel keeping it at 100% it will reduce the charge input until the battery falls to 80%.

58 minutes ago, pcaouolte said:

Did you reset the battery monitoring system after fitting the new battery? The smart charge system will be trying to maintain the battery at about 80% charge, if it's already at 100% charge the system doesn't want to waste fuel keeping it at 100% it will reduce the charge input until the battery falls to 80%.

Yes, done that now. I wasn't aware of how this charging system works. Our older Focus is more suited to us old folks. Thanks for your help. Sorted.