AN1012

Battery backup current - predicting data retention time

Doc ID 6395 Rev 4

9/33

Figure 4.

Predicted battery storage life versus temperature

3.2

Calculating storage life

Only the user can estimate predicted storage life in a given design because the ambient

temperature profile is dependent upon application-controlled variables. As long as the

ambient temperature is held reasonably constant, the expected storage life can be read

directly from Figure 4 on page 9. If the battery spends an appreciable amount of time at a

variety of temperatures, the following formula can be used to estimate predicted storage life:

where,

●

●

●

For example, consider a battery exposed to temperatures of up to 90 °C for 600 hrs/yr, and

from Figure 4,

●

●

●

T is 8760 hrs/yr;

●

●

The predicted storage life evaluates to:

This predicts that the storage life, in this particular case, is at least 14 years. This is,

therefore, better than the normally accepted life time of 10 years.

AI01024b

20

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90

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8

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TEMPERATURE (Degrees Celsius)

10

20

30

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SL50% (AVERAGE)

SL1%

1

–

t

1

T

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1

SL

1

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×

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⎜⎟

⎛⎞

t

2

T

-----

1

SL

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×

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…

t

n

T

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1

SL

n

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×

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++

+

1

–

600

8760

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1

1.8

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×

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⎛⎞

8160

8760

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1

28

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×

⎝⎠

⎛⎞

+