Wet cell, gel and AGM batteries are all types of batteries that may be found on a narrow boat. Wet cell batteries are the most widely used type of battery, however with developments in technology, some narrow boat owners are considering the benefits of using gel or AGM batteries.
Battery Types… Wet Cell
So called because they use a liquid electrolyte. In the case of batteries for our narrow boat market, we use lead acid wet cell batteries.
The active ingredients are lead for plates and sulphuric acid for the electrolyte.
Cells produce 2.1 volts with internal construction determining amp output. We commonly find cells cased together in 6‘s to form the familiar 12VDC starter/leisure battery. Pay more for a tougher/heavier construction & you will usually gain in terms of product life cycles.
Regard has to be given to safety. They can spill electrolyte if mishandled or poorly installed and produce potentially explosive gases during heavy use. They are heavy so consideration should also be given to maintenance access and ballast requirements when planning your installation on your narrow boat.
Wet cell lead acid batteries are available for user self maintenance or sealed for life maintenance free. Whilst the convenience of maintenance free is hard to argue with, the very nature of the wet cell means that longer life will usually be achieved if you are prepared to do simple checks and topping up. This is especially the case for the leisure bank as the many charge/discharge cycles will inevitably deplete the electrolyte to gassing over time.
For this reason these types of batteries must always be installed in ventilated battery boxes in conjunction with the BSS on your narrowboat.
If purchasing a new canal boat, wet cell batteries are usually included as standard. However there is normally an option to upgrade to Gel or AGM batteries, your narrowboat builder would be able to provide the cost of any upgrade. If you are deciding on your specification for a sailaway canal boat, consider carefully which batteries are the best option for you in terms of requirement and budget.
Battery Types… Gel
Gel batteries are a form of lead acid battery in the class of VRLA batteries. Gel batteries are becoming more common place on narrow boats as technology steps up.
VRLA stands for Valve Regulated Lead-Acid.
Gas Recombination Under Pressure…
As we have seen, the discharge/charge process produces hydrogen gas. In a common wet cel battery, this gas is vented to the outside air. In a VRLA battery, the electrolyte is effectively immobilised therefore trapping the hydrogen close to the plates. During the charging process the trapped hydrogen is recombined and the cycle starts again. VRLA battery types are hermetically sealed to allow this recombination to occur under pressure.
With a gel battery the liquid sulphuric acid/de-ionised water electrolyte is gelified by mixing it with a form of silica. The resulting mixture is a jelly like substance which is immobile and therefore cannot be spilled when tipped over. They differ very slightly in their components when compared to wet cell lead acid batteries, but this is a chemical difference which allows for the gas recombination to occur as mentioned above.
Faster Charging…But be Careful…
A benefit of this chemical difference in plate construction is that VRLA batteries can be charged much quicker the conventional wet cells. However charging has to be controlled as over rigorous charging can mean that gasses build up too quickly for recombination.
The batteries have a safety valve which allows minute levels of gas to escape in the case of excessive overcharging or high charge rates. Additionally overcharging will lead to premature failure, another good reason for ensuring your charging system is suitable for your battery type.
Check Your Charger is Compatible
Gel battery charge acceptance is better than wet cell so they will recharge quicker. Wet cells loose up to 20% of their charge energy into heat whereas gel cells will loose 12% on average. They will also discharge naturally at a lower rate so can be left off charge in storage for a bit longer than conventional wet cells. However, they use slightly lower charging voltages than wet cells so it is imperative to ensure your equipment is compatible with this technology in order to get the most benefit from a gel lead-acid battery system.
Maintenance Free, at a Price…
Gel batteries can be used in any orientation and are maintenance free. Whilst maintenance free may be an advantage for some on a narrow boat, it can also be a disadvantage in that electrolyte levels cannot be topped manually and as a consequence, battery service live may be shortened. Good quality gel batteries are more expensive than their wet cell equivalents.
Battery Types… AGM
An AGM battery is another lead-acid battery to be found in the sub group of VRLA batteries (see Gel Batteries above). AGM batteries can offer narrowboat owners more options when specifying power systems.
Absorbed Glass Mat…
AGM refers to Absorbed Glass Mat and the clue is in the definition. Very thin glass fibres are woven into a mat and used as a separator to hold the electrolyte. Although the glass fibres themselves do not absorb the electrolyte, the matting itself holds enough electrolyte in close contact with the plates for the life of the battery. The plates of an AGM battery can be any shape with some cells being flat or other types being rolled.
Vibration and Spill Proof…
AGM batteries really are a step up in the evolution of lead-acid batteries when compared to both wet cells and gel batteries. They are spill proof and much more vibration and impact resistant than their counterparts, which is ideal on a narrow boat installation.
Conventional Charging Systems…
One big advantage over gel batteries is that AGM batteries use the same charge parameters as wet cells so they can be a genuine drop-in replacement.
Remember, they are a form of VRLA so attention still has to be paid to charging rates. Too vigorous overcharging and the gases will not recombine fast enough and you will ruin the battery bank (not to mention your personal Bank)!
Battery Types… Lithium-Ion
Most batteries are based around lead-acid; even newer Gel and AGM batteries use this basic chemistry. However emerging in to the market over recent years are lithium-ion batteries, which are better known for being used in mobile phones, tablets and laptops.
Lithium-ion may be seen by some boaters to be the ultimate battery set up for a narrow boat, but unfortunately this indulgence will come at a price to match currently and you could be looking at a several thousands of pounds for a set up.
However, there are, of course, many advantages to lithium-ion batteries:
- Depending upon the model, you can expect a 360Ah unit that holds around 5kWh of usable power (more than six conventional 110Ah 12v lead acid batteries).
- Unlike conventional lead-acid batteries, you can get almost all the stored energy out of them without damage. Lithium Ion batteries can be discharged to 80-90% with no issues. It is not advisable to regularly discharge lead-acid batteries below 50% of the original capacity.
- You can also charge them over 2000 cycles, with a complete re-charge taking only around 1 hour to complete. Lithium Ion batteries can have up to 3 times the life span of conventional batteries.
- Space saving – Lithium Ion batteries are considerably smaller and lighter than lead acid batteries. They can be at least half the weight of a traditional battery!
- In our Charging section we discuss the 3 stage charge process – bulk, absorption, float. With conventional lead acid batteries it can take a long while to reach the Float stage due to the internal resistance of these batteries. With Lithium Ion batteries, there is no internal resistance, therefore almost no absorption time, meaning they reach 100% charge in very little time.
- Lithium Ion batteries will also maintain their voltage during use. You will not experience any lose of capacity with heavier loads, for example if you are using high power items such as washing machine, microwave, hairdryer etc. Conventional lead acid batteries will suffer greatly under heavy loads.
There has been several reports in recent years of the dangers of Lithium Ion batteries in mobile phones etc, however be assured that the marine standard Lithium Ion batteries are a different chemical grade, look out for Lithium-iron phosphate (LiFePO4) which claim to be the safest on the market.
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