The answer to this question is somewhat counterintuitive. Battery pack gas-gauge ICs, such as the one used in the Impulse 6000D/7000DP, use a complex algorithm to estimate battery-charge state, taking into account time, temperature, and current flow. The self-discharge estimation (i.e., how much charge the battery loses over time during periods of non-use, sometimes called "shelf-life") is particularly sensitive to battery chemistry, and the shelf-life of today's NiMH cells is significantly longer than the algorithm built into the gas-gauge ICs can accommodate.
When an Impulse 6000D/7000DP is left idle for a few weeks and then powered-on, the battery charge level might be reported as 55 % when the true charge level might be 80 %. If the battery is then completely charged, which requires a 20 % increase in battery charge level, the charge level is only reported as 75 % (55 % plus 20 %).
To correct the reported charge level, use the "Train Battery" feature. To access this feature, press the [SETUP] key, then the [F1] softkey(labeled "Battery"), then press the [F3] softkey (labeled "Train Battery"), then follow the instructions presented on the screen. This procedure can take overnight to complete.
To keep the reported battery charge level as accurate as possible during extended periods of non-use, the Impulse 6000D/7000DP should be left connected to mains power via the battery charger with the unit powered off in an ambient temperature of 15Â° C to 26Â° C (60Â° F to 78Â° F). This will continuously trickle-charge the battery (the charge-status LED on the rear panel will be green) to keep both the actual and estimated battery charge level at 100 %.