First of all, why do you need to replace your battery. Battery loses its efficiency over time. You might find your unit no longer holds charges. Mine happen to be around 4 years old and it fails to last me a 2 hr ride with NAV on. It is time for a battery replacement. Bear in mind, you do not have to do this yourself. If you are not comfortable opening up your unit, any phone repair shop can do this and it should take no more than 1 hr to complete this job. However, if you are a handyman (woman), the following guide will help you to tickle this task.
Tools that you need: Replacement battery, Removal tools (mine came with the replacement battery), Hair Dryer or Heat Gun, Glue (Loctite Extreme OR E6000)
Open up the unit. This is the most challenging part of the job. Please process with caution. Warm up the unit’s all sides with a heat gun, this will soften the glue around the unit. Carefully NOT to overheat it, as it can damage the LCD. Once it is warm ( again, DO NOT OVERHEAT), it is ready to be pry open. Pry opens the unit starting from the edge using a specific prying tool. You want to be extra careful because the front panel has an LCD in it. While you are prying the face plate, use the suction cup to help open up the unit.
Once the unit is open, cautiously fold the front panel to the side. To access the battery, you need to remove 4 screws that hold the motherboard.
Next, disconnect the battery connection to the motherboard. There is a small sponge over the connection. Remove it and put it aside. Pry away the black connectors from the motherboard.
Next, use the pry tool to slowly remove the battery. DO NOT use any heat gun to soften the glue that holds the battery. Heating the battery is extremely dangerous. After removing the battery, cut the wires that connect to the unit’s speaker. Please use common sense. DO NOT cut both Negative and Positive wires together. You can create a short or worse, an explosion. In addition, you would want to cut it as close to the battery as possible. This way, it will have enough wires for reconnection to the new battery.
Final, reverse all procedures. Last step, before closing the unit, you want to make sure the unit can power it on. If not, go back and recheck all connections. If everything is a go, start placing glue around the unit and close it up to complete the job. At this stage, use some amount of weight to sit on the front panel while waiting for the glue to cure. Do not worry about the glue coming out from the gap. These glue are gel type and it can easily be removed later on once it is cured.
Tips: I had a difficult time connecting the connector to the motherboard. What you should look for, it's simply snap it back in place and use its original sponge. Once the unit closes up, the sponge will hold the connection which keeps it in place.
Additional Tips: I prefer Loctite Extreme than E6000. It is less messier and it has more control when apply it.
I replaced mine with an aftermarket battery. It is rated 2100 mAh and it is 3 times its original Garmin battery’s capacity. I managed to turn on my GPS NAV while having the unit at 80% brightness for a 2hr ride. At the end of the ride, I managed to have 80% left in the battery. I’m extremely pleased with the new aftermarket battery performance.
Alternatively, you can replace it with the original Garmin battery. It is rated 750mAh and you will need to pay a premium for it.
Belows are the links for the tools and components
Electronics Opening Pry Tool Repair Kit (if your replacement battery didn’t come with it) https://amzn.to/3f5QlW7
Aftermarket Garmin Edge 520 / 520 plus / 820 Replacement - 2100mAh https://www.aliexpress.com/item/4000539930416.html?spm=a2g0s.90423126.96.36.199c64c4dTeXPxq
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