How do I Replace the Batteries in ECO2?
PRC Battery Specifications
If a battery is over 18 months old, is holding a charge less than the specified run time and a battery test has been completed to confirm the actual run time, it may be time to replace the battery. If a battery is over 18 months old, but the run time is still within specifications, it may not need to be replaced.
If a device requires repair, the repair technicians will make a recommendation to replace the batteries if the batteries are over 18 months old. If a device comes in with a power problem, the battery will be tested to determine if it requires replacement. If a device comes in for issues other than power, the battery will be tested and will only be replaced if the battery fails that test.
If a device comes in for warranty inspection (to inspect the device prior to reinstating a warranty that has expired), the battery may be replaced as part of the inspection if the batteries are 12 months or older, at the discretion of PRC.
Part Numbers for Replacement ECO Battery Packs:

Part Number14856 is the Removable battery: this is the large battery on the left with a flexible tab on the end you can pull to remove the battery. When replacing the battery, make sure it clicks into place before replacing the door.
Part Number 14857 is the Internal Battery: this is the smaller battery on the right. This battery remains in the case and should not be removed unless replaced. Take note how the white connector is plugged in before unplugging, since it will need to be plugged in exactly the same way to prevent damage to the device.
Removing the Battery Door:
With the battery charger unplugged, slide the door to the right until it comes off.

Take off the small remaining battery door by removing the phillips screw using a #1 phillips screwdriver, then slightly push in on the door and slide right.

Remove the old batteries and install the new battery packs exactly the same way they were removed. Make sure you tuck the tab for the Removable Battery slightly under the battery pak so you will be able to read the battery status on the end of the battery pack. Replace the battery doors. Your new batteries may have some charge in them when received, although it is recommended to fully charge the batteries overnight before using the ECO2.
Special Note about Battery Disposal:
If the batteries in your device need to be replaced, dispose of the old batteries properly. Follow the regulations of your community, state or country for the disposal of batteries.