Battery Types V 1.3  2013  Dominic de Vries

 

We recommend to use LIFePo4 battery cells or lead acid deep cycle batteries, which are both the most reliable and suitable battery types for boat propulsion.

 

Deep Cycle Batteries

This are lead acid batteries similar to a car battery, but optimized for a use without maintenance and less sensitive to low discharge compared to conventional lead acid batteries. But all lead acid batteries offer only around 36-38 Watthours per kg weight when fully charged. Lead acid batteries can be discharged to 90-95% of their capacity, but only within 10-20 hours. So, if you need all the power in 1-2 hours, only 65% of the capacity is available and the voltage drops slowly with discharging. Also the lead acid batteries offer a life span of 500-800 cycles only but are the cheapest option.

 

 

Lithium Batteries (There are different types!)

 

 

Li—ion Batteries

These are all battery types where lithium ions move between the positive and negative electrodes. There are types with high energy densitiy like the Lithium Cobalt Oxyde batteries which offer over 200 Watt hours per kg, but can be instable and dangerous for larger applications.

IMPORTANT: Some systems like chargers or BMS units only indicate „Li-Ion Batteries“. There is an important difference in the cell voltage of such batteries which can range from nominal 3.2 to 3.7 volts per cell. So a LiPo setup can damage a LiFePo4 battery!

 

LiFePo4 Batteries

Lithium Ferrite Phosphate batteries offer the safest and most economical option for boat batteries. The initial price is still 2-3 times higher than lead acid, but as those batteries last for over 2000 cycles at 1/3 of the weight (100 Wh / kg) the costs over a life cycle are less. Also these batteries can be discharger to over 90%, so less capacity is required.

 

 

LiPo / Lithium Polymer Batteries

Developed from high density Li-ion batteries these batteries keep the electrolyte in a polymer composite instead of an organic solvent. This makes them safer and cheaper to manufacture.

Those batteries offer  a high energy density and are mainly used in consumer electronics (laptops, mobile phones etc.), but also in some electric vehicles. The batteries offer a life span of 400-800 cycles, but are quite sensitive to mechanical damage. temperature, under– or overcharge which reduces their life cycle. The energy density ranges from 120 to 200 Watthours per kg weight. We do not recommend these batteries for the use on boats, as they are not as reliable and safe as the LiFePo4 batteries and more expensive.

 

Future

There are promising projects, like the thin film lithium battery which is announced to offer over 10000 cycles or special high density capacitors. But this will not happen over night!