FCP and other Youtube videos do a nice job of showing replacement. I am replacing the battery. So far the Message is gone but I'm letting the battery charge before running a full test. The PC board was pretty beat up but I had purchased the batteries over half a year ago so decided to install it anyways.
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Same type of battery
https://www.ebay.com/itm/2-Pack-3-6V....c100005.m1851
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Partial fender liner removal.
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Tried to chisel with hammer and pry bar first. Cut slot, hammered and pry bar again. The vise grip is what loosened it.
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Cut along gray plastic where it meet the black edge of the case with a hack saw. Rotary tool only melts the plastic. Used a blade to clean the 2 contacts for the battery.
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Cut wires on battery and wired in series to double the voltage from 3.6V to 7.2V. Twisted wires together and used a glued filled shrink tubing to hold them together instead of soldering.
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Had to trim sides of battery connector in order for it to fit inside the connector of the PC board. Battery is positioned to go inside the case. Trim / remove protruding plastics in the case which held the old battery.
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Used a flexible rubber tube to separate battery from PC board besides cushioning inside the case. Clamp the case together and seal with silicone.
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