The marine battery must meet the following environmental technical conditions: to adapt to vibration and shock. Vibration can make the fixed or connected parts of electrical equipment loose, and make the structure of parts damaged or failed. Therefore, it is necessary to have anti loose measures, vibration reduction or isolation measures, strong mechanical structure resistant to vibration and impact, and adapt to tilt and swing. The continuous tilt and swing destroy the balance of the force in the normal static position, produce additional force on the moving parts, resulting in equipment failure or damage; adapt to the ambient temperature. Environmental temperature has an important influence on the performance and service life of electrical equipment. The ambient temperature includes air temperature and sea water temperature; it is suitable for humid, salt fog, oil fog and mould environment. The humidity, salt mist, oil mist and mould of the ambient air make the insulation performance of the insulation materials of the electrical equipment decline, and make the metal parts rust and corrode. The wet salt spray forms a wet leakage film on the surface of the insulating material, and the organic acid is secreted by the mould under the hot and humid conditions, which aggravates the wettability of the surface. The adhesion of oil mist and dust to the surface increases the surface leakage, and hinders the heat dissipation to increase the temperature. The moisture molecules infiltrate into the cracks and pores of the insulating materials, which increases the leakage current and reduces the insulation resistance.

Depth of discharge (DoD) refers to the percentage of electricity taken out of the battery in the rated capacity. The discharge depth of the shallow cycle battery should not exceed 25%, and the deep cycle battery can release 80% of the electricity (Ball & Risser, 1988). Because the battery life is affected by the average state of charge of the battery, we must coordinate the relationship between the cycle depth and capacity of the battery when designing a system.

The discharge depth of a cell or cell is used to measure the amount of released charge. It is expressed in the form of A.H. DOD can also be expressed in the form of percentage. Lead acid batteries usually express their DoD in the form of percentage. It is more useful to express DoD in the form of a · h, so that the combination of state of charge (SOC) (expressed in percentage) and DOD (expressed in a · h) can transmit more information than both indexes expressed in percentage.

This is obvious for batteries with an actual capacity greater than their nominal capacity (for example, nominal 100A · h, actual 105a · h). When a battery with a rated capacity of 100A · h releases a charge of 100A · h, SOC will change to 0, and the DOD of the battery can be expressed as 100% or 100A · H.

But if you want to release all the charge of the battery, but the SOC of the battery is still only 0 (because SOC cannot be negative), and the DOD of the battery marked with percentage can only be 100% (because the DOD marked with percentage cannot be higher than 100%). However, if a · h is used, then the DOD will become the correct 105a · H.

It is more useful to know that the DOD of the battery is 105a · h than to know that it reaches 100%. This is because even if the DOD of the battery reaches 100%, the power can still be released from it. Another important reason for the expression of DoD with a · h is that the discharge depth of the battery is independent of its discharge rate.