If you take the capacity down to 90% DoD – when the lights start to dim – you will probably get 10-20 cycles at most. Regularly take this down to 80% DoD and the figure will drop to 25-30 cycles, at which point you will probably only have 50-60% of the original maximum capacity remaining. The cheapest lead-acid leisure battery on sale in your chandlery will probably give you at best 100-125 cycles at 50% DoD. In addition, the number of useful cycles any battery will give you over its lifespan is governed by how low you take its charge each time, known as Depth of Discharge (DoD), and how fast you take the power out. Thus your nominal lead-acid battery capacity will have to be even greater if you are regularly taking out high currents. This becomes especially significant if you are powering an inverter, or driving an electric boat. Typically a battery that will give you 100Ah if it is discharged at 5A, ie over a 20-hour period, will only give you 80Ah if you discharge at 20A, ie over 5 hours, and 50Ah if you discharge at 100A, ie over a nominal 1 hour.
Some lead-acid technologies will improve on this, but at greater cost.Īt the same time the faster you take power out of a lead-acid battery, the less overall capacity you will get. This is because most lead-acid batteries should not be regularly discharged to below 50% of their capacity, or their cycle life will rapidly diminish.
The generally accepted rule of thumb with lead-acid is that your battery pack capacity should be double what you are likely to use in one day, or between recharges. So is it time for you to switch from the 19th century technology to the 21st? Yet lithium boat batteries offer much better performance and lifespan, but at a much higher up-front price. Boat owners have long relied upon the lead-acid battery to start their engines, run electric lights and, these days, to power inverters to run household items such as kettles, microwaves and more.
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