Rechargable Lithium batteries in RTC circuits

It would depend on the way its used. If its used in a PC where the RTC runs off the computer's power supply most of the time, it'll get almost shelf life. On the other hand, if it is the only power the life will be a lot shorter.

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Service to my country? Been there, Done that, and I\'ve got my DD214 to
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Michael A. Terrell
Central Florida

Well, you used to get almost shelf life out of the batteries that weren't rechargable, so I don't know what is different. At least with the old batteries you would have a holder. Now you solder the rechargable in. Rechargable or not, won't it still die?

Think about it. Any cell (or group of cells) can only be recharged so may times. If the equipment is used all the time the cell isn't doing anything, so it should be close to shelf life as long as it isn't constanly charged at too high a rate. The old PC motherboards that used a 3.6 VDC NiCad for the RTC charged at a very low current. If it was dead, the computer had to be on 12 to 24 hours to fully recharge.

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Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

That is what bugs me. The thing is now a soldered in part and no one has convinced me that it will last longer than the product lifespan just because it is rechargable.

-------------- That is what bugs me. The thing is now a soldered in part and no one has convinced me that it will last longer than the product lifespan just because it is rechargable.

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Rechargeable Li+ should normally be recharged on a CCCV scheme (with an RTD for thermal sense). If you are going to (or need to) recharge a different way, check with the manufacturer. Trickle charging of Li+ is

*not* a good idea.

If the only thing it's running is a RTC in power off, then it's perfectly possible a non-rechargeable cell will meet the requirement, saving money and parts. A typical RTC draws less than a microamp in standby from 3V, so if you were using a small Li non-recharegeable with

120mAh capacity to run only the RTC (typical coin type 16mm diameter), then you have 120,000 hours of life ~ 13.7 years. So is it worth a rechargeable? Only if you have to run other things from that battery, imo.

Cheers

PeteS

A lot of PC motherboards were destroyed by leaking NiCads. it was made even worse because anyone could pull a shunt from two pins on a header and plug a cheap alkaline battery pack to the board so it would work for a while, leaving the bad battery pack to ooze and eat the traces.

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida