A battery's lifespan
A very common question we are asked is how long a battery will last and what is the maximum life span that can be expected. The life of a battery is substantially defined by the number of charging and discharging cycles. A cycle is defined as the following: Discharging a battery to 20% capacity and then recharging it back to a 100%. If the battery is only discharged to 50% and then fully recharged, it is half a cycle. Depending on their design and construction, the on-board batteries have a certain number of cycles and thus an appropriate life expectancy.
A car battery
is designed to last about 50-80 cycles.
This sounds very little, but in practice it is more than enough. While a very high current is required to start your engine, the start-up only takes a very short time - resulting in only 0.0001 cycles. This means that the engine
can be started between 50,000 and 80,000 times. The life expectancy of AGM and gel batteries
is estimated at about 300-700 cycles. That means, if the battery is only 50% while dis- and recharging, the result are 800 to 1000 cycles. While dis- and recharging at 25%, the result are 1,600 to 2000 cycles. Therefore, when used in normal on-board operations
, batteries can have a life span of around 7 years
. After reaching the stated number of cycles, 80% of the battery's capacity remains. At this point, battery manufacturers consider the battery as used and to be replaced, but this does not mean that you have to replace it. Let's compare it to a diesel tank: your tank is in new condition and has a capacity of 100 liters; after about 7 years, the tank has "shrunk" and only takes 80 liters.
Questions about the warranty
come up regularly in connection with the life span of a battery. If a vendor promises a warranty of 3-5 years, this is simply untrustworthy. If the battery ran through a complete charge cycle of about 400-500 charges in the first year due to intensive use, it is basically used up and has done its job. That's like buying a new car and driving over 100,000 km in the first year and then complaining that the tires are worn down.
Care and maintenance of batteries.
Each battery, regardless if it is a lead-acid, AGM or gel battery gets damaged when it is completely discharged and not recharged immediately. In addition, a significant shortening of life expectancy occurs. If possible, don't discharge your batteries completely, a remaining capacity of approximately 20% should always be maintained. In case of total discharge, please ensure immediate recharging of the battery.
AGM and gel batteries do not require any maintenance. However, the connections should be periodically checked and the batteries must be fully charged. All batteries have a certain amount of self-discharge. This amount is so small for AGM and gel batteries that they will even survive a winter break without being connected to a charging device (e.g. Marine battery charger). AGM and gel batteries cannot freeze in winter storage and thus do not need to be removed from your boat in winter.