8821 batteries life & battery models.

[LSVCH]

We have poor performance in our 8821 series phones, like many seem to have had or have currently. Checking articles on the cisco webpage, we see battery life rated 13.5hrs or 9.5hrs "talk time" depending on which link you click. Most of our several hundred devices can't go 24hrs standby with 15 minutes of talk time. In doing some research, I've noticed sites list batteries, as 3.75v 2000mAh as well as 4.35v 2060mAh. Hard to tell if there actually is an extended battery (as they had for the 7925 series (1100mAh to 1450mAh) when the cisco site states "Rechargeable Lithium ion 4.35V, 2060mAh smart battery (minimal capacity 3.8V, 2000mAh)", is there a fabled 4.35V, 2060mAh "smart battery" or is all of this just manufacture wording?

[Haydn Andrews]

There have been a large number of known bugs with the 8821, that you might be hitting.

This one could be the cause CSCvf59659

Reference around the battery size refer to this https://bst.cloudapps.cisco.com/bugsearch/bug/CSCvf14721/?rfs=iqvred

Some other things you could try:

1. Extending the DTIM period to 2 instead of 1 on the WLAN so the phone wakes up less frequently to check for data.
2. Setting scanning mode to Auto instead of Continuous. This is only recommended for deployments where clients don't roam a lot whilst on calls as it reduces background scanning for roaming targets

There is a really good reference for best practices for VoWIFI here.

What version of WLC and CUCM are you running?

Also have you confirmed that RF coverage meets the Cisco VoWIFI guide? https://www.cisco.com/c/en/us/td/docs/wireless/controller/8-5/Enterprise-Mobility-8-5-Design-Guide/Enterprise_Mobility_8-5_Deployment_Guide/Chapter-9.html