Sentry-2412 (BatteryDAQ) detected a high Internal Resistance for one battery while voltage is normal. 

Voltage (V)	Internal Resistance (milliohm)

Tried to verify with a portable battery tester, it won’t measure correctly for this battery.

Battery looks perfect from front view but it has a crack on the side.

Measured with a multimeter, this battery has about 800mV AC ripple on posts while others only 10mV.

Most portable testers utilize AC method for lower cost, they cannot work with high ripple input due to the signal range limit. They may give wrong result or random data for a bad battery like this one when measure it online.

All BatteryDAQ’s product utilize the proprietary pulsed DC technology. It costs more in production but ensures consistent data for online measurement crossing wide range UPS and charging systems.

The rule is simple as Four-Terminal sensing (4T Sensing): to separate current-carrying path and voltage sensing probing.

For Sentry battery monitor installation, keep in mind that the sensing O-rings have to be in close contact with connection bar without any washer in between. (O-ring shall not be placed between connection bar and battery post. That will compromise battery bank connectivity).

Stainless steel bolt and washer have high resistance. If installed as “RED”, battery#1, #6/#7 and #12 will have wrong measurement, which will lead to wrong battery health “SOH” estimation and trigger alarms.

Enjoy your fine work!

Using BatteryDAQ’s cloud, scan a 2D barcode on Sentry monitor or battery rack, and your smartphone will show real-time battery data and graphs.  Bank voltage, current, temperature, individual battery voltage and internal resistance etc. (SOH%, SOC% and Runtime minutes for Telecom models) are all available.