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Boat batteries again

Hi, Graham & Rupert, with reference to my last question on boat batteries on 25th March 2012, can you please give me any further info as follows.
Thank you both for your advice, I have everything to gain and nothing to lose.
If it all goes wrong I have been looking at battery types, Deep cycle wet lead-acid or Gel Deep cycle types Both types are sold as sealed and maintenance free, however all batteries gas when charging and must vent. Are sealed maintenance free batteries really maintenance free? or able to be topped up and worth buying, I do not mind paying a bit more for them if they give me better service than open type. Are you able to recommend your preferance Gel v Wet lead acid and any makes.

Asked by: David Anderson  | 5.48pm, Tuesday 27 March

WW says:

You are correct in saying that all lead acid batteries will produce hydrogen gas when fully charged or faulty and thus battery compartments need to be vented. Gassing causes water loss which needs to be replaced.
Gel batteries are so called because the electrolyte (acid) is turned into a jelly like substance when the cells are flooded. If these batteries gas, the bubbles disturb the structure of the gel and cause loss of capacity. They must therefore be charged at a lower voltage to ensure this does not happen.
Conventional wet batteries are more robust and get my vote, although they will invariably need topping up. The 'maintenance free variety' are usually only guaranteed as such if the charging regime is similar to gel batteries so that gassing never occurs. Whether they are able to be topped up is down to the case design, but is usually possible as they have to be filled at some point!

Rupert Smedley  | 4.56PM, Wednesday 28 March

I agree with Rupert. My preference would be for open cell, lead-acid batteries but these are becoming increasingly hard to find.
I have a set of Elecsol open cell batteries on my boat and these have lasted far longer than batteries are normally expected to. This is partly because they are not greatly stressed and because they are charged and topped up regularly. I know I will have to replace them at some time but I don't know what with as Elecsol only seem to make 'maintenance free' batteries in that size now.
One manufacturer of electronic equipment who will remain nameless advises you should buy the cheapest battery possible and reckon on replacing them more frequently. The argument is that, unless batteries that cost three times as much last three times as long, they are not worth it, and he finds that most don't.

Graham Booth  | 11.50AM, Thursday 29 March

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