THM1176 battery discharge problem

22.04.10

THM1176 battery discharge

Since the introduction of the THM1176, we have observed problems with the battery in the handheld discharging too quickly. Possible solutions are at hand!

Socket Mobile - the manufacturer of the handheld computer used in the THM1176 - has released an important Customer Service Notice concerning problems with the 2600 mAh battery. This Notice addresses a number of different failure modes and causes, and also includes important suggestions for improving the battery life.

The problem we have been confronted with most frequently is that the battery discharges overnight, while the unit is not being used. I quote:

Midnight Power-On issue: Microsoft has a function built into all Windows Mobile operating systems. This function will wake-up the SoMo (but not turn on the LCD display) at Midnight every day. It can sometimes be seen by the flashing green LED indicating WLAN activity – if WLAN was on at shutdown time. The unit will turn on for a time equal to the backlight disable setting. Depending on applications on the SoMo device, the unit may be put in an “on” state and drain the battery.

As it turns out, for the THM1176, the factory configuration was to never disable the backlight, so in principle, the unit will turn on at midnight and never turn off. This is easy to fix: In the Backlight control panel (Start menu -> Settings -> System tab -> Backlight), check the box "Turn off backlight if device is not used for..."

Many other problems are due to poor contacts of the battery terminals. To fix for these problems, Socket Mobile proposes a spacer that, when glued to the top of the battery, improves the pressure on the contacts. We have never seen these problems, but if you experience the symptoms described in the Notice, Metrolab can supply you with one of these spacers.

The notice also has important suggestions concerning how to extend the battery life. The most important parameter is the number of charge/discharge cycles; this battery has a recommended life of about 500 cycles, which should last about 2-4 years. But storage conditions also affect battery life. Optimally, batteries should be stored with a 30-40% charge, at 5°C (40°F). Storing a battery fully charged at high temperatures will cause permanent capacity loss. This is exactly the case, for example, if you leave the handheld computer plugged into the charger with the screen left on. According to the Notice, this can reduce the life to 6-12 months.

Metrolab continues to look for ways to extend the battery life. We greatly appreciate your patience and feedback in this matter, and apologize for the inconvenience we have caused by our inadvertently poor choice of configuration options.