hi folks,
I have a 55' narrowboat with four leisure boats and one starter. There is also a heart interface/charger 1800 ems. I have had my new batteries for about two years now and they don't seem to last as long now, so, looking in 'the manual' it talks about equalising the batteries. My questions are(as it takes about nine hours) do I undo the cell tops and leave open when equalizing or do I just loosen them as it only says to check that they are topped up? please help, many thanks, steve.

If the batteries are lead acid they should have a vent, if not loosen the cell tops to allow the hydrogen to escape.
Remember no smoking, naked lights, or operating any electrical equipment that could cause a spark and have plenty of ventilation while the batteries are gassing.

You can calculate when the batteries are gassing by the specific gravity and cell temperature. I can't remember the equation but its should be easily found on the internet or at the local library.
Remember that hydrogen is lighter than air.

Hydrogen gas has a distinctive smell/taste, you can smell it and taste it at the same time.

I have a 57' narrowboat which we only bought last October. It has 1 starter and 3 leisure batteries which were renewed before we took delivery. I hope we don't have any problems for some time, but I've never heard of the term 'equalise the batteries', and it might be useful in the future. Can you please explain?