Whether or not the boat remains afloat or ashore, action to preserve batteries is the same:
Clean off the tops - any dirt or salt will retain moisture and allow the battery to discharge - surprisingly quickly sometimes. Check the electrolyte level in each cell, and top up with distilled water so that the plates are covered.
Charge them up fully, and store them in a cool dry place - the garage will do. Once a month, put them on charge for 12 - 18 hours to top them up. Otherwise, buy a Gunsons Charger from Argos for around £20, and leave them permanently connected. Periodically check that the electrolyte is not dropping away. DO NOT do this with the ordinary cheap battery chargers from the car stores - they will overcharge and damage the batteries if left for more than 24 hours or so, as they have no form of charge rate control.
A battery left to its own devices loses its charge through internal losses, and can discharge itself enough to damage the plates over six months, and its capacity will be reduced the longer it is left uncharged. Irreversible chemical changes take place. Battery 'freshening' treatments may reduce this effect temporarily, but once left discharged for any length of time, the battery will be effectively written off, and even if resuscitated will soon give up altogether - usually at the worst moment!
An interesting point though.....I am paranoid about keeping my batteries fully charged but since moving from a marina with shore power to a swinging mooiring I more or less accepted that I could not achieve this. It was only when both batteries were flat the other weekend that it occured to me that it was'nt difficult to take them home to look after them!. After all, I'd brought them out to the boat, hoisted them aboard with a rope through the handles, and often do the same for the 32kg gas. (I have a hard dingy and am about 400m from the shore)
One, a 'BSX leisure' at about 5 years old is showing 12.56 v after 24hrs rest. ...probably ok for one more season.
The other, a MAC about 3 years old is showing 12.75 .....we'll see.
I agree with above, just one additional point - as a general point on battery maintenance, before bolting posts and terminals together again give all surfaces , screws, bolts etc a smear of vaseline to prevent corrosion.
Hi Jean ,
What type of batteries do you have? If you have sealed batteries the advice your getting could damage them, and at worst they could explode!!
If you can specify the make, size and type, the better will be the advice you will get.
All batteries lose charge when not being used at the rate of about 1% per week.
It is probably inadvisable to leave them on charge permanaently with any battery charger, but they will need to be charged regularly
The batteries should be deeply cycled - to the 80% discharge level -every four to eight weeks; ideally, just before they are equalised. (I have never done this on purpose - however, once or twice by mistake.) This will increase and/or maintain capacity.
The next two items apply to all flooded lead/acid batteries.
When topping up the batteries with distilled water, do so only after a FULL charge, to a level 1/4" above the plates (if you do this before a full charge the odds are the electrolyte will bubble over).
Battery acid, when it dries on the tops of the batteries, conducts electricity.
This leakage will run the battery down and create potential electrolysis problems, if the batteries are in any way connected to the hull or through hull fittings.
Clean the tops with a solution of baking soda and water in a spray bottle, or Windex (which contains ammonia - a base - which will neutralize the acid).
The battery conditioning is an important factor in the life of batteries - you should be able to expect 7-10 years use out of reasonably well manufactured heavy-duty or traction batteries especially if you use a "smart" regulator.
Thanks Charles - some interesting points there, and I agree with your point about the advisability or otherwise of leaving them on permanent charge - unless the charger is specifically designed to give a float charge, which the Gunsons unit is - and it seems to work. Hence my warning not to use other types of cheap charger in this way.
I am not very happy at the idea of running batteries right down to 80% discharge - it depends on the type of battery. Ordinary car batteries - 'Starter batteries' - will suffer a loss of capacity every time they are discharged below 50% charge - the degree of loss depending on the rate of discharge, and the length of time they are left before recharging. Cheaper models may even begin to deteriorate at 75% charge which is a bit worrying when most alternators will only recover to around 90% charge unless fitted with smart regulators.
Deep cycle and traction batteries may well benefit from a regular charge/discharge programme, and any battery will suffer if left idle for extended periods without being made to work. However, Car batteries, and most 'Leisure batteries' which are commonly found in boats because they are cheaper and more readily available, will be damaged by deep cycle discharging.
Equally they will be written off within a couple of years if not cared for over the winter lay up period!