We had a number of systems at a previous employer. Mixed results if I'm honest - a lot of work to install and I'm unconvinced about the data we got from it.
The company we dealt with isn't trading anymore, but Alber are the current kings of this field.
Concur with ScottyUK above on a number of points..
1. We used to do open circuit voltage only testing, which I agree was not particularly informative about the battery condition, only for those customers not willing to pay for periodic load testing which does give good results regarding battery bank condition.
2. With the advent of the test technology developed by Alber in their Cellcorder family, the Alber Cellcorder C-300 did prove out to be a reliable indicator of battery run time capacity and end of life.
Statement 2 above was from detailed measurement data collected over a period of 20+ years (initially with the practice of recording only cell voltages (and load testing for customers willing to pay). About midway through this 20 year period, Alber cellcorder technology became available and measurements with the CRT-300 model was done over a customer base of around 100+ sites. Current model:
One caveat.. there was quite a bit of snake oil out there with various cell restance measurement methodologies, too lengthy to get into in this post. A read of Alber's whitepapers (although it looks like they've been simplified from earlier research papers they used to post) is recommended..
will likely expand the market for online monitoring for open circuit failures of battery strings. Eagle Eye monitors will appear to meet the NERC requirements. I have requested money to install open circuit monitors at several substations next budget cycle. Since these monitors cost almost as much as the battery cells, I don't know whether the battery budget will get doubled or whether the battery cells will get replaced half as often.