Battery voltage / amp. readings

[boy boater]

I would be grateful if someone could explain to me what the readings on the voltage meter and ammeter should be for my domestic battery when the engine isn't running, i.e. no charge from the alternator. Should the voltmeter show a steady 12v until it is fully discharged, or does the voltage drop off gradually? About a week ago I turned on some cabin lights, they were quite dim and the voltage meter showed 10v. At the same time the ammeter needle was flicking from side to side (+ / - 25 amps about). I put the battery on charge, it charged at about 25 amps initially, dropping to about 3 amps after about 5 hours when I had to disconnect the charger. The voltage shown on the voltage meter was then 12v. I have not been to the boat since to see if the battery has held its charge. As a final observation, there would appear to be a slight discharge 0.5 amp from the battery (as seen from the ammeter) when no domestic circuit is switched on, e.g. fridge, lights, etc. Is this in order, please?