Most HP  / Agilent E8285A Test Sets with V2.04 or earlier firmware get this on screen warning. The "AA backup battery low" warning is to alert the user that the back up battery to the Memory Battery is low. HP issued an official service bulletin to ignore this warning because the unit already has a coin battery to back up the memory and the AA... warning is for another backup battery to the coin battery.
    First of all, the E8285A has no AA batteries. The AA.. warning is a cary over from the 8935 firmware warning. The E8285A does have a BR-2/3A  3V lithium battery soldered into the power supply regulator board at the rear of the unit. The first remidy is to replace this battery. These batteries are readily available from Mouser Electronics for about $5.
    Another remidy is to apply a voltage to the circuit board memory battery + to fool the E8285A. This is easily done by removing the 2/3A battery, adding an isolation diode and 680K ohm resistor in series from the +9 volts on the regulator board to the memory battery + solder pad. The E8285A - AA warning will now go away.
    The E8285A can also have a "low memory battery" warning. This differs from the AA battery warning. The "Low memory battery" indicates the battery on the memory board is failing. This is the main user memory battery. This one is a CR-2477HFN (CR-2477 with solder tabs) and is available from Mouser and DigiKey for about $4.
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