BOS LE300, the marine lithium batteries that really work

6 mins read

A good six months have passed since the beginning of our test with the new BOS LE300, the lithium batteries designed specifically for boating. And, above all, an entire season of cruising has passed on board the Daydreamer which, as always, spends most of its time at anchor, the best way to test and stress the use of the battery pack dedicated to on-board utilities.

BOS LE300 lithium-ion battery test

Let us tell you straight BOS-LE300-Smart-Battery-System away, without mincing words: these batteries work brilliantly. They drastically change on-board energy management, eliminating all worries about consumption. At sunset, our volmeter regularly read 13.5 V (compared to the classic 12.8 V of traditional batteries) while the following morning, after keeping the fridge, the anchor light and the fans on (it was really hot this summer), the voltage was never less than 12.8 V.

This created a virtuous cycle whereby, apart from one occasion, on the only rainy day of the season, we never had to turn on the engine (or generator) to recharge the batteries.

In fact, the energy from the 150w solar panel, which produces about 60/70 Ah during daylight hours, was always enough to recharge them.

This success and advantage is mainly due to the following factors:

  • Lithium batteries have a higher operating voltage than conventional lead-acid batteries, and are therefore able to store the excess energy produced by solar panels, in particular the differential between 12.8 and 13.4V

  • The BOS LE300s discharge completely with priority over the AGM batteries to which they are connected (which conventional batteries cannot do), which means that the first 100 Ah are drawn exclusively from the lithium batteries, thus preserving the charge of the conventional battery pack.

BOS LE300 Smart Battery System: how it’s made

BOS-LE300-Smart-Battery-System-installation The BOS LE300 Smart Battery System is an advanced energy storage system consisting of individual 12 V lithium intelligent battery modules, each offering 28 Ah of capacity and 12.5 A of current. These lithium batteries can be used either to increase the total capacity of existing lead-acid battery packs, or to study and optimize the operation of a new battery pack when replacing or installing it for the first time.

The primary function of this system is to replace the discharge of lead-acid batteries, while keeping them at the highest possible voltage, exploiting the capacity of lithium batteries to deliver amperes, up to full discharge, without decreasing their voltage.

In a nutshell, the BOS LE300s can be fully discharged while the lead-acid batteries remain charged and healthy! What’s more, this technology is plug-and-play, i.e. the installation of BOS LE300s does not require any additional charger. Installing them simply means putting them in parallel with existing batteries, making it easy to adopt this system.

The version installed on the Daydreamer, i.e. the one comprising four BOS LE300 modules capable of delivering a total of 50 A and a capacity of 102.4 Ah, has a retail price of around €1,500 + VAT.


Installation Video

Technical Specs

System voltage

12 VDC

Norminal voltage

12.8 VDC

Voltage range

11 -15 VDC

Battery packs used in LE300

IFpR/26/65 [8p/4s] E/-20NA/95 LiFePO4 rechargeable battery

Nominal lithium capacity

28 Ah / 358 Wh

Usable lithium capacity

90% (25.2 Ah / 322 Wh)

Numbers of cycles at room temperature

>3000 complete cycles

Continuous charging current

Max. 12.5 A between 5 and 40°C, at higher and lower temperatures current is limited.

Battery efficiency

> 90%

Housing dimensions

175 x 229 x 67 cm


3.4 kg

Recommended wire size

1.5 – 4 mm²

Ambient temp. (operation & warehousing)

-20 – 50 °C ambient temperature with

 maximum battery life at 15 – 25 °C.
 Warehousing temperature 10 – 30 °C.

Low and high temperature protection,

Temp. sensor prevents lithium battery charge under -5°C or above 55°C cell temp.

heating, charging & dischargingCharging starts once cell temp. is higher than -5°C.
 Device has an integrated heating that is active between -20°C and 10°C cell temp.
 Discharge possible between -20°C and 60°C cell temp.
 At cell temp. below -20°C and over 60°C system is running in pure lead acid mode for higher battery lifetime.

Lithium cell balancing

Battery management inclusive balancer

Protection features

Overcurrent, overvoltage, short circuit, deep discharge, wrong polarity protection.

Operation mode/compatible external batteries

Works in combination with any 12 V lead acid battery & lead acid charge controller.

Connection possibilities

Packs can be connected in parallel with each other (see exemplary parallel combination in the table below).

Max. parallel LE300s

In standard version, a maximum of 24

 LE300 can be connected only in parallel, higher quantities possible after consulting BOS partner.

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