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What is in a sealed battery that enables it to be used without a regular top up like the more cheaper lead acid type

Asked by: george  | 3.34pm, Sunday 2 February

WW says:

A sealed lead-acid battery has a greater volume of electrolyte in its simplest forms... More expensive ones have recombine structures to prevent water loss and hydrogen loss. However, if you charge them at too high a rate they will gas and produce hydrogen, losing electrolyte. For most boats, the open-cell batteries are a better bet, with a longer life.
You very rarely get a proper deep cycle battery that is sealed for life... Most are open celled units.

Mark Langley  | 6.24PM, Sunday 2 February

Sealed lead acid batteries employ much the same technology as conventional cells, but are sealed to prevent spillage of acid. They do incorporate a valve which will vent gas if they become faulty or are overcharged which will produce hydrogen gas. Since they are usually very difficult to top up with distilled water, the recommended charge voltage is reduced slightly to prevent gassing, which causes loss of electrolyte and creates the need for topping up.
As Mark says; open cell batteries are a better bet.

Rupert Smedley  | 6.31PM, Sunday 2 February

I agree with Mark and Rupert.
It is a great shame that more and more battery manufacturers are switching from batteries that can be topped up to those that are 'maintenance free'. All too often, this means that the cannot be maintained, in which case, if some of the electrolyte is lost through charging at too high a rate, the battery has to be scrapped.

Graham Booth  | 10.43PM, Sunday 2 February

Looking at your question again, I wonder if you are thinking of more expensive types of battery like Gel or AGM.
With Gel batteries, the electrolyte is in the form of a gel rather than a liquid. AGM stands for absorbed glass mat and these batteries have a glass mat which holds a small amount of acid between the plates.
This means that they can be installed in their sides if necessary without the fear of spilling as an open cell lead acid type would. It is also claimed that they last longer and do not lose their charge so readily if left unattended.
However, they are generally two to three times the price of a lead acid battery so you have to be convinced that they will last two to three times longer before you invest in them.

Graham Booth  | 10.59PM, Sunday 2 February

I meant 'installed On their sides'.

Graham Booth  | 11.12PM, Sunday 2 February

Readers say:

Thanks for the info and i will take it onboard and use it the ones in question are brit marine sealed and maintainance free and i realise you cannot judge each dealer so i will ask around and go for open cell

george  | 11.48PM, Sunday 2 February

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