Application Note 155

Battery Charger Functions for 20/20 TDR, E20/20 TDR and VIA Echo Instruments

Written by: Paul DeWinter for

AEA Technology, Inc.

Applicable Models

20/20 TDRs (rechargeable models only)

E20/20 TDRs (all models)

VIA Echo Network Analyzers (all models except MRI)

General Information

The battery charging function and charging LED status indictors for both the E20/20 TDRs and VIA Echos work the same. The 20/20 TDRs do not have an LED status indictor, but the charger function is identical. Check their status in F2 Battery Menu. What is different between the instruments is the operational time based on a full charge of fresh AA batteries. Charging can be done while operating the instruments or using the DC Vehicle Charger, but in both cases charge times will be greatly increased.

Charging Status LED for E20/20 TDRs and VIA Echo Instruments only

The battery charger works in four stages as indicated by the Charging Status LED:

  1. FLASHING RED – Normal when the DC input power is initially connected or the instrument is cycled ON or OFF during the charging cycle. This is the Battery Check stage. The TDR is looking at the battery voltage to set the charging program. It also checks for alkaline cells installed and will terminate the charging if they are detected.

  2. SOLID RED– this is the Pre-Charge and Charging stages. The current into the battery starts at about 128 mA. The LED remains solid RED for a period of time as the battery charge increases to 400 mA (if the TDR is off), this starts the full charging stage.

  3. FLASHING GREEN – Batteries have reach 95% of full charge capacity and charger switches to trickle charge to top the batteries off. The instrument can now be taken off charge and will be operational to about 90% of its fully charged time (see chart on page 2).

  4. SOLID GREEN – Batteries are fully charged and the charger provides a Trickle Charge to maintain full charge and prevent overcharging.

Optionally, if the instrument is ON the charging status can be checked in the Battery Menu as follows:

20/20 TDRs – Press “F2” key, scroll down to Battery Menu and press the right arrow key.

E20/20 TDRs – Press “Meter” key, scroll down to Battery Menu and press the right arrow key.

VIA Echos – Press the “F4” key, scroll down to Battery Menu and press the right arrow key.

NOTE: If the instrument is OFF and charging and is then turned ON, you may need to wait up to 30 minutes to get correct charging status. To quickly get a reading on the batteries’ voltage level and estimated run time unplug the charger and wait 30 seconds for the status to update.


Recommended Charge Times

If the batteries are low or very low, recommend 12hrs to reach fully charged (solid green LED). If the batteries have moderate charge (40% +) they should be fully charged in 4-6hrs. The instruments are useable for limited periods of time with a partial charge or at 95% charged (Green Flashing LED). Recharging time for the instrument’s batteries will vary with their charge at the start of recharging, age of batteries, and environmental temperatures. The chemistry of the batteries will NOT permit recharging if their ambient temperature is below 32o F (0o C) or above 122o F (50oC). See Battery Menu status for “HOT” or “COLD” The instrument may feel very warm during charging, particularly near the end of the charge stage and my temporarily go into “HOT” status suspending the charge until they cool.

Estimated Continuous Operation Time with Fresh Batteries


Full Charge

95% Charge

Moderate charge

20/20 TDRs


~7.2 hrs


E20/20 TDRs


~5.5 hrs


VIA Echo


~3.0 hrs


Backlight use and brightness level will reduce these times by 15-25%

All instrument models can have their NiMH batteries temporarily replaced with AA alkaline batteries. Fresh alkaline batteries will provide full charge run times.

WARNING – Do NOT mix alkaline and any rechargeable batteries in the instrument. If you do install alkaline cells, go to the instrument’s Battery Menu, scroll down to BATTERY TYPE and select ALKLINE or NONE to turn off the battery charger. This will prevent accidentally attempting to charge alkaline cells which could cause severe overheating and outgassing of the batteries.

If you have any questions with this information/instructions or need assistance please contact us at 1-800-258-7805 or +1-760-931-8979 or by email at

Related Application Notes

AN151 – Using Batteries in AEA Technology Instruments

AN153 – Cold Weather Operations for AEA Technology Instruments