Sokkia SDR33 CMOS Lithium Battery (CR1/3N)

> How long the SDR33 CMOS battery usually lasts in your experience?

Mine last for months as long as there are fresh 9V batteries in the unit. Once the 9V's go dead, the lithium backups seem to be not far behind. If the SDR33 is going to sit unused for quite some time, it's better practice to take all the batteries out if you have all the data downloaded.

I don't know but mine somehow drains so fast. 🙁

I bought a pair of new ones about two years ago, took them out of the SDR33 and stored them in the case after only using them once. I took them out and they were dead, evidently from old age. The 9-volts of the same age were still very good. You can find the lithium batteries pretty cheap on eBay.

Batteries of all types do have a shelf life some much longer than others. Be sure your supplier is selling you fresh batteries, not ones that have been sitting around for a couple of years. I've purchased different types of button type batteries in multi packs because it was a good deal only to discover the ones that have been sitting unused in the package for two or three years are dead. Package price still a good deal even if some of the batteries died compared to buying individually but I'll refrain from buying large multi packs in the future.