Posted: Sat Sep 11, 2010 1:17am

I have a problem with sulphation of the battery terminals. The boat (and batteries) are two years old. I have 6 cabin batteries, one engine start, and one for the bow-thruster. The problem was initially thought to be a small (25amp) battery charger - this has been replaced by a new 60amp charger about six months ago, but the sulphation is worse than ever. The boat is used as a liveaboard, mostly on a marina berth hooked up to a 240v landline. My local boatyard are due shortly to remove, clean, and test the batteries and reduce the 'cabin' bank from six to four. Do you have any other suggestions ? Graham Jeffery

Posted: Sat Sep 11, 2010 9:34am

I think you have got your terms mixed up. You would not see sulphation on battery terminals BUT you would see corrosion which is not uncommon. Sulphation is a term that applies to happenings inside the batteries NOT the outside. First of all why on earth are you reducing your bank size? The slower you discharge a bank in relation to the size of the bank the greater the effective capacity it has. This means that your present (say) 660Ah will be able to supply your loads for far longer than simple maths implies than the new 440Ah bank. With shorepower the batteries should still be in fair condition. My best suggestion is that you start doing some routine maintenance of your batteries. If these are wet open cell batteries someone has quiet possibly overfilled them. If they are sealed batteries I suspect over enthusiastic application of a spanner has cracked some of the battery lids around the posts. First of all ensure open cell batteries are kept topped up to the correct level. If there is no level indicator in the cell then fill to between 3 & 6mm above the separators (the plate like things you can see down the hole). Remove ALL the negative terminals and then the positive ones. Taking great care to prevent it getting into the cells use very strong, hot bicarbonate of soda solution to dissolve the corrosion. Use abrasive paper to clean the insides of the clamps and the battery posts to bright metal. Now to try to minimise the corrosion. Apply a very liberal coat of Vaseline to the posts. Refit the clamps (all the positives first) and then smear the Vaseline that oozes out of the clamp around the clamp thread and into any conductors where the insulation has moved back from the terminal. Ensure all the terminals are covered in a film of Vaseline. Unless you have an absolutely horrendous electrical load I do not see why a 25 amp charger would not meet your needs as long as it is left on all the time. I also suspect that the equalisation charge cycle of your new charger might be making the corrosion worse without a film of Vaseline to protect the terminals from the acidic gassing. I am left with a feeling that there is much you have not told me about the situation and also you may not be getting the best impartial advice. Tony Brooks