on 08/02/2018, Johnny B Good supposed :
You need to be aware that SLI LA batteries aren't designed to cope with
continuous float charging for month after month after month periods at
the classic (and seemingly more benign) 13.8v level. Six months seemed to
be the point where such 'gentle float charging' would ruin them (a bunch
of four connected to an APC SmartUPS2000 2KVA/1500W rated UPS... Twice!).

You are spot on with that. I have several such batteries and having
wrecked a few in the past, by using 13.8v 'maintenance' chargers, my
regime now is one of bringing them up to a full charge once every 1 or
2 months. The diodes trick will only work, where the charger will
charge irrespective of seeing a voltage across its output.