Battery Types

There are many different battery types in use today all designed for different applications. This artical focuses on those of interest for a Hybrid Marine Propulsion System.

Hybrid Marine's parrallel hybrid system is capable of charging any type of battery. The system incorporates a four stage charging algorithim when operating in generate mode and includes the inputs necessary to connect an external Battery Management System to control both Charging and Discharging of the battery by the hybrid system. The Victron Invertor Chargers supplied as part of our systems also have these capabilities ensuring that the whole system can work with any battery technology, both now and in the future.

Flooded (wet) Lead Acid Batteries


This is the so called "milk float" or "fork lift truck" batteries but they find use in many industrial and traction applications. The Flooded lead acid battery is a very mature technology offering known performance a good life time and an excellent price- performance ratio and is our standard solution for all systems except seagoing boats.

Wet cells generate Hydrogen and Oxygen durring charging which has to be properly vented for safe operation, and will require regular topping up with deionised water to maintain the electrolyte levels in the battery.

When properly maintained Flooded Lead Acid batteries offer excellent performance and are ideally suited to the Hybrid Propulsion system. We have systems with batteries over 10years old still in use.


"Maintenance free" Lead Acid Batteries

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These Batteries are sometimes refered to as "Sealed" but technically they are all Valve Regulated Lead Acid (VRLA) batteries. Although the basic chemistry of a VRLA battery is the same as other Lead Acid batteries the difference is that the electrolyte is retained in the cell by being absorbed into a glass Mat ( Absorbed Glass Mat - AGM) or as a Gel (Gel Battery) aand so cannot spill if the battery is tipped up, or in some cases mounted on its side (see manufaturers data sheet) This property means that AGM and Gel batteries are commony used in seagoing and sailing boats to avoid battery acid spills.

These batteries are generally designed to be maintenance free and do not require the electrolyte topping up like Wet cells. This is achieved by recombining the Oxygen and Hydrogen generated during charging back into water inside the cells. During charging the gasses are held under pressure inside the cell and there is a Valve which will release this pressure if it exceeds the batteries design limits. Once gas has been vented from the cell it cannot be replaced so this will lead to the battery drying out and eventually becoming unusable. It is essential to manage charging of this type of cell carefully to minimise water loss and ensure the cells are not damaged by excessive charge currents or voltages.

AGM and Gel cells are generally more expensive than the equivalent Wet Cell and offer shorter lives. They also have significant charging limitations which can limit thier use in high power applications.


Lead Acid Variations

lead carbon

Although Lead Acid batteries are a mature technology there are continuing inovations in attempts to improve the design. Recently Lead Carbon batteries have been in the news are these are claimed to offer improved partial charge and discharge performance in a VRLA format.

Lead Carbon batteries are more expensive than Flooded cells but offer the advantage of being maintence free. These batteries are another VRLA variation and must be charged with care to avoid excessive gassing, and ventilation requirements need to be carefully considered

Although there are some impressive claims made about the life expectancy of these batteries they have not yet been around long enough for this to be proven in the field, and especially in a Hybrid system. Hybrid Marine do not currently reccomend Lead Carbon batteries.



Lithium Ion Batteries


Lithium Ion batteries have become widely available in recent years as they have been adopted in portable battery powered technology such as phones, and are used in Electric Vehicles. There are a number of differing chemistries used under the banner of "Lithium" or "Lithium Ion" batteries and these offer different energy densities. In general the higher the energy density the higher the price and the more volatile the battery becomes. (think of exploding smartphones for example).

Lithium Iron Phosphate Batteries

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In a marine environment safety of the battery is paramount, no one wants a battery fire while sailing offshore, or in any boat that is also your home, so this generally means using metal cased batteries or selecting Lithium Iron Phosphate (LiFePO4 or LFP) chemistry which is regarded as being stable and safe in most circumstances.

LFP batteries do offer a size and weight saving over Lead Acid, but in heavily ballasted canal boats this is not generally an advantage. LFP batteries are maintenance free and can be left partially charged  without affecting the long term life. However these advantages come at a cost with an LFP system being at least double the cost of an equivalent Lead acid system

Hybrid Marine can supply LFP batteries as part of a system but in most cases where weight is not a consideration Lead Acid is still the most cost effective solution.

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