CR1220 Battery in Asset Tracker - Usage Concerns

The datasheet for the Asset Tracker shield mentions the following about the CR1220 battery.

“Inserting the coin cell powers up the internal RTC of the GPS module and also help retain the satellite data in its volatile RAM. It is highly recommended that you have this battery plugged in at all times to bring down fix times.”

I’ve been using this battery and it’s been working fine along with my external GPS antenna to get fast fix times.

My concern is-- if the device is deployed remotely and I can’t easily access it for a long period of time (maybe years), can I expect that CR1220 battery to eventually die and require replacement? If so, what kind of differences could I expect in fix time if the battery is either dead or not inserted? It may not be feasible to reclaim the Asset Tracker(s) often just to replace the coin cell.

Any insight would be appreciated. Thanks!

Mike

@mike_b
You can expect the battery to eventually run out. In cases where the battery is dead or not present, the fix times from a cold start (power off - power on) will vary depending on the location and visibility of the horizon. It can be from 35 seconds to upto a few minutes. The backup power consumption for the RTC is only around 7uA; so you can try powering this up from your main power source instead of the coin cell.

Regards,
Mohit

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@mohit, will the VBAT/3V3 bridge need to be removed in order to prevent the controller from leeching the battery too.

NVM, it’s only feeding the GPS chip and not VBAT/3V3 :blush:

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Thank you for the clarification, Mohit!

@mohit, @ScruffR, I have a similar question that this thread gets 90% of the way to answering. I’m using an E-Series module with my own ublox chip (mimicking the Asset Tracker V2). Can I just short the LIPO power in (I’m using the standard kit’s 2 A-h Li battery) to the V_BCKP of the ublox instead of using a backup battery? It looks like the Li battery can get charged above the ublox chip’s max V_BCKP voltage, so maybe the answer is an obvious “no” based on that.

I could instead short the E-Series’ 3V3 output and the ublox’s V_BCKP, I suppose. 3V3 stays high even in SLEEP_MODE_DEEP, right? I just checked that with a multimeter but am asking to make sure I’m not missing something silly as I am a nearly complete noob. This post is motivated by my desire to keep V_BCKP getting what it needs even when the E-Series is in SLEEP_MODE_DEEP.

Thank you!

Hello Phil,

On the asset tracker, the 3V3 is connected to the V_BCKP. You can very well do that in your design as well.

Regards,

Mohit

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Ah, okay, thanks—sorry I missed that. I see SJ1 (solder jumper, I guess?) now to allow for either the coin cell or 3V3. I knew the coin cell was a backup but I guess it’s almost like a backup backup. Appreciate your help.