Hyndai Excel 1998 battery drain

Hi
Before I ring an auto elec., any ideas with this power drain/charge problem?
Excel 98 1.5 litre dohc, non-carb, (electronic)
Had RACV out as battery went flat whilst driving.
Alternator belt was apparently loose. RACV did a quick check of alternator and seemed okay.
Charged battery. Next day same problem. Other symptom that may not be related but occurred at same time is that engine doesn't return to idle quick enough. Engine takes about 5 extra seconds to return to idle. This means stop-start traffic driving is not comfortable - rev's too high to nudge car forward in second gear. Car battery is tiny. About three years old?
Any help much appreciated.
Cheers
Dave
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Battery holds a charge well, according to ammeter on battery charger

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