Lifetime expectancy of the Renata Lithium battery on recent PCD compared to previous PCD generations

FAQ #101780

 

There are two main reasons to explain this fact:
 
- The supervision function was improved
The new battery supervision function sets the battery under a very small load to predict the end of battery capacity. In term of battery capacity, this additional load is negligible, but allows the system to warn before the battery is really empty. That gives enough time to exchange the battery and preventing memory lost. This is not the case on the previous generation, where only the voltage was supervised.
 
- There is more memory to support
The recent systems have much larger memory; the resulting standby current to be supplied from the Battery increased short the time duration.
 
Summary of working principle with the Lithium Battery
System with passive battery supervision applied on the following PCD’s:
PCD1.M130, PCD1.M135, PCD2.M110, PCD2.M120 and PCD2.M150
The voltage of the battery is supervised.
SBC advise to change the battery all 1 - 3 years.

System with active battery supervision since 2001 applied on the following PCD’s:
PCD1.M2xxx, PCD2.M170, PCD2.M480, PCD2.M5xxx, and PCD3.Mxxxx 
If the 24VDC power is switched on, then the voltage of the battery is measured during short time all 12 seconds where the battery is submitted to a small discharge.
This allows to warn the application program before the capacity of the battery reach its end.
We estimate that in this case the battery has still two days of reserve capacity for the changing of the battery.
In most recent PCD's the battery change can be done from end-user keeping the 24VDC power supply of the PCD switched ON.
If during the battery change, the 24VDC power supply of the PCD remains switched ON then there is no lost of the SRAM content (means that the PCD medias does retain there values)

A lost of the SRAM content (PCD medias like registers, flags and the application program [application program only if there is no application program stored in the Flash memory] does occurs only if the 24VDC power supply is switch off during the battery change.

The specifications in the manual concerning the typical life time of a Renata battery is still correct (1-3 years).

Today, on April 2013 we are able to give more precise lifetime expectancy for the battery for PCD’s produced since July 2012:

	Service conditions	Lifetime expectancy of the battery
a.	continuous power OFF	24 Months
b.	power ON 8 hours on 5 days a week	34 Months
c.	continuous power ON	80 Months

However SBC advices to preventable change of the Lithium battery all 5 years

Note that these values are set conservatively; longer lifetime of the battery can be achieved in the practice.

For PCD’s produced before July 2012, above mentioned times could be shorted by 20% due to larger SRam standby current.

The value of standby current is verified on each device during the production.