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BOS, energy on board: lithium and lead together make the difference


The German BOS, with its LE300 Smart Battery System, brings on board medium-small boats a hybrid system that makes the most of the characteristics of lead-acid and lithium batteries


With all the new equipment “coming on board” and the ever-increasing level of comfort, energy boats are never “satiated”.

The LE300 Smart Battery System from the German company BOS makes it possible to expand the overall energy storage capacity and rationalise its use without having to modify the classic 12V electrical system; it is a plug-and-play hybrid system that combines lead and lithium technologies, exploiting the best of both.

Details of operation

At the heart of the system are its LE300 Lithium-Iron-Phosphate (LiFePO4) smart batteries of 12V, nominal 28 Ah, and effective 25 Ah and 300 Wh.

They are compact and lightweight (229x175x76 mm for 3.4 kg), modular and can be stacked, side-by-side and installed in several blocks according to the space available on board. Once connected in parallel with the lead-acid battery (AGM, GEL, or wet cell), the system is ready to work. Up to 24 LE300 modules can be connected in parallel and only in rare cases there is a need to change or modify parameters on the charge controller.

A management software is Integrated into the LE300 that optimises the storage capacity and charge and discharge cycles of the entire system, exploiting the full potential of the batteries. Discharge priority is given to the BOS lithium modules that control the voltage of the lead-acid batteries and keep them at maximum voltage. The latter are used as an accumulator and backup, and come into operation in the event of energy peaks (at the end of the peak, the LE300s pour energy back into the lead-acid batteries, returning their voltage to 13V. This avoids numerous charge-discharge cycles to the lead ones).

Compact and light, a LE300 module measures a small 229x175x76 mm for 3.4 kg

The charging process

During the charging process, the lead-acid battery reaches a constant voltage charge and the charge current reduces. The smart battery system detects this and the LE300 absorbs the available energy that is not taken by the lead acid battery.

As a result, both batteries are charged at the maximum available charge current, until they are full. Especially with solar power, the full potential of the sun can be realised in every moment, while the lead acid battery gets many charging hours to reach 100% every day.

With the inbuilt heat elements, the system also has great benefits in extremely cold environments. The integrated cell heating has time to heat the lithium cells while the lead can receive high current even in freezing cold. This allows to charge the system without negative impact on cycle life.

System redundancy

Up to 24 LE300 modules can be connected in parallel

For added safety, the BOS system is redundant: each module of the LE300 has its own built-in Smart Battery System, in case one module fails, the others continue to work without any problems.

The batteries are designed and tested to work even under extreme conditions and are protected against overcurrent, overvoltage, short circuits, deep discharge and reverse polarity.


INTERVIEW - Martina Pons, owner of M&M Marine Store
On the nautical market, BOS started operating in Germany in 2019 and in the following years expanded into foreign markets.

We got to know the BOS LE300 batteries at the Genoa Boat Show in 2021 and immediately started offering them to our customers.Martina Pons, owner of M&M Marine Store in Imperia

M&M Marine Store is a retail outlet for nautical accessories strategically located halfway between the two ports of the Ligurian city, which for over 11 years has been serving boats from small fishing ones to superyachts of over 60 m.

Who are your customers?

We sold them to several owners of sailboats between 12 and 14 m, all of whom needed to increase their energy storage because they spent a lot of time in roadsteads while on their cruises.

One of our owners’ problems was the limited space available: the batteries of the BOS LE300 were an excellent solution that allowed them to double the energy on board even in tight spaces.

And in addition to space, the low weight of the BOS LE300 should also be considered, compared to that of a lead-acid battery of the same amperage: we are in the order of 1/3.

How do you size the system?

Once you have decided how many amps you want on board, you have to take into account the fact that the lead-acid battery does not deliver the nominal amps: in fact, once it reaches 50% charge it has to be recharged, so the real amps available are about half of the nominal ones.

For lithium ones, on the contrary, the nominal power corresponds to the actual power. For example, if I have a nominal 100 Ah lead-acid battery on board (which I can therefore only use for about 50 Ah effective) and I decide to double the total energy storage, I will have to mount a pair of LE300s, which are 28 Ah each. This way I will have 100 Ah effective.

How do you install the system?

The strong point of the BOS LE300 is its ease of installation. In practice, it is such a plug-and-play solution that all our customers have installed it themselves without having to call in a technician. No need to change the charger setting or anything else: simply connect the lead-acid battery and the LE300 in parallel, with the cables supplied with the BOS batteries, and the system is ready.

Installation of the LE300 is extremely simple, simply connect the lead-acid battery in parallel with the BOS modules