Richard Russell laid this down on his screen :
What's the consensus of opinion on whether it's OK to leave a car battery on
continuous (float) charge? Wikipedia says 'batteries kept on continuous
float charge will have corrosion in the electrodes and result in premature
failure' but other sites seem to recommend the practice when the vehicle is
in infrequent use.

I have three batteries kept almost permanently on a float charge and I
have done this for many years without any problems. Just make sure the
float charger outputs an accurate float voltage.

I bought a couple of the Lidl chargers on sale a few weeks ago -
judging by the tests I carried out, these charge fully, then fall back
to an perfectly accurate float charge voltage.

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Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk