# RTC battery life calculation

Discussion in 'General Electronics Chat' started by jonisonvespa, Feb 6, 2013.

1. ### jonisonvespa Thread Starter Member

Mar 25, 2012
49
0
ok

after getting fantasic advice regarding a selection of the battery for my rtc, i tryed to work out how long my battery would last, could someone please check my maths please

thanks very much

my RTC runs at 200n

1 nano = 0.000 000 001
200 nano = 0.000 000 200

Say the Battery is 100ma hour,

so devide 0.1 by 0.00 000 002 = 500 000 total hrs

=500 000 devided by 24 hrs in a day = 20833 days or

57 years,

Last edited: Feb 6, 2013
2. ### #12 Expert

Nov 30, 2010
18,076
9,676
You slipped a digit. 200 nano is 0.000 000 2

That's 57 years.

3. ### JMac3108 Active Member

Aug 16, 2010
349
67
As you can see, these calculations ausually end up showing that the shelf-life of the battery is the limiting factor, not its capacity.

But be aware than in your actual circuit you may have other small leakage paths that draw current in addition to the 200nA from the RTC. For example if you are diode-ORing the battery with another power source to the RTC you may have some leakage through the diode when the other power source is turned off.

bug13 likes this.
4. ### jonisonvespa Thread Starter Member

Mar 25, 2012
49
0
yes thanks i saw that after i posted it

thanks very much, i intend doubling the battery to 200ma

thanks very much