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UNDERSTANDING FACTORS THAT AFFECT CHARGING TIME
UNDERSTANDING FACTORS THAT AFFECT CHARGING TIME
The time it takes to fully recharge a battery depends on several factors including:
1. Battery Depth of Discharge
The greater the depth of discharge, the longer it will take to fully charge a battery. For example, a
battery discharged to a level of 50% will take about twice as long to fully charge than a battery
discharged only 25%.
2. Battery Size
If charged at the same current, a larger (higher capacity) battery will require more time to fully charge
than a smaller (lower capacity) battery. This difference can be overcome by charging larger batteries
at a higher current.
3. Battery Age and Condition
As a battery ages, its internal resistance willl increase, impacting its ability to accept current. This
effect is particularly noticeable in batteries that have not been well-maintained over their life.
4. Battery Type
Some battery chemistries, such as AGM and gel, have lower internal resistance which means they can
accept charge better without generating damaging heat. Such batteries can charge up to 2 times
faster than traditional wet battery types.
5. Charge Rate
The charge rate is measured in amperes (A). A battery charged at a lower rate will take longer to fully
charge than a battery charged at a higher rate. This does not mean that one should always charge a
battery at the highest ampere available as this can cause overheating and premature battery failure. A
battery should be charged at a rate appropriate for its size—a good, safe rule of thumb is about 1/10
its Amp-hour capacity (e.g., 100 Ah battery x1/10=10 A).
6. Cold Temperature
Cold temperatures slow down the chemical reaction that takes place inside a battery when it is
charging. Charging a battery at a cold temperature can greatly increase the amount of time required to
charge the battery. Ideal charging temperature is between 10 to 25 C (50 to 77 F).
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