Braun Oral-B Genius/Smart Type 3765 Battery Replacement

This guide will show you how to open and dismantle the Braun Oral-B Genius 9000, Genius 8000, Smart 6000 and Smart 6 electric toothbrush models and repair them by fitting a replacement Li-ion battery. These are expensive, top-of-the-range toothbrushes so they are well worth repairing!

This battery replacement guide is only for Genius and Smart toothbrushes from Braun Oral-B that are marked with “Type 3765” on the bottom. Click the photo below to enlarge it and compare it to your toothbrush:

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For other toothbrush makes, models and type numbers the battery replacement procedure is different so please see our other guides to toothbrush battery replacement for these toothbrushes.

The basic method is:

  • Open and dismantle the toothbrush handle
  • Desolder PCB connections
  • Remove the old battery
  • Solder in the replacement toothbrush battery
  • Reassemble handle

The type 3765 toothbrush battery replacement process is documented in detail below along with lots of photos. Click on any photo to enlarge it.

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Disclaimer

Any damage or injury to yourself, your toothbrush or anything else is entirely your responsibility. This guide is for professional, educational usage only and is offered without guarantee or liability. Lithium-ion (Li-ion) batteries are dangerous if short-circuited and can go into thermal runaway and self-ignite if you do not observe all handling precautions.

Tools, Parts & Equipment

  • Braun Oral-B Genius/Smart type 3765 electric toothbrush
  • Original charger
  • Soldering iron with needle/cone tip: Electronics grade (about 18-25 watt)
  • Solder: Lead-free silver solder with a flux core is recommended
  • Solder sucker (also known as a desoldering pump) and/or desoldering braid/wick
  • Needle nose pliers
  • Craft knife e.g. scalpel, snap-off, retractable or Stanley type
  • Small flat-bladed screwdriver: 2 to 4mm wide
  • Large blunt flat-bladed screwdriver: 4 to 6mm wide
  • Miniature side cutters
  • Adhesive putty such as Blu Tack to hold the toothbrush to the work surface
  • Replacement Li-ion battery: Available from ToothbrushBattery.com here

How-To

To start with, remove the brush head from the top of the handle and stand the toothbrush, tip downwards, in hot tap water for 5 minutes to soften the plastic ring.

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Using the large flat-head screwdriver start to pry off the plastic ring from around the shaft. The ring is stepped so press down into the soft casing to get under its lower edge. A screwdriver with blunted edges is less likely to mark the toothbrush, and prying from the back side of the handle will hide any marks.

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Store the removed ring carefully.

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Stand the toothbrush in hot tap water again, tip upwards this time, for another 5 minutes to soften the seal around the base cap and the internal plastic clip.

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Dry the handle with a towel then put it on its charger (unplugged.)

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Carefully bend the toothbrush backwards so the base cap is levered open.

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Lift the toothbrush off the charger and remove the base cap. Be careful not to lose the spring!

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Push the top metal shaft into the main body of the toothbrush handle so that the toothbrush innards start to slide out.

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Fully remove the inner workings of the toothbrush from its casing.

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Unclip the white plastic LED surround, starting at the upper end.

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Time to get your soldering iron warmed up now! A soldering iron with a fine needle/cone tip is recommended.

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Locate the positive battery connection on the PCB (arrowed below.)

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Remove some of the solder from the connection using the soldering iron and a solder sucker or braid. Then reheat the solder joint and simultaneously pull the battery’s solder tag away from underneath using the small screwdriver to bend it downwards.

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Locate the two copper charging coil wire connections at the lower end of the PCB (arrowed below.)

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Remove most of the solder then lift the wires clear of the PCB using the tip of a craft knife.

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Release the white clips holding the black plastic coil support in place.

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Slide the coil support off the end of the PCB.

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Locate the negative battery connection (arrowed below.)

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Desolder the tag and bend it away from the PCB.

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Fold the negative solder tag well clear of the bottom of the PCB.

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Fold the battery’s positive solder tag as close as possible to the body of the battery.

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Slide the battery towards the bottom of the toothbrush by a few millimetres so that the positive tag is clear of the central white plastic structure. We will be rotating the battery in place.

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Rotate the battery about an eighth of a turn clockwise (looking from the bottom of the brush.)

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The positive tag might be touching the PCB, but there is no electrical hazard as the negative tag is not connected to the PCB.

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Locate the M+ and M- motor connections on the PCB (arrowed below.)

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Partially desolder the motor connections, enough to let you lift the PCB slightly. You might need to unclip the nearest white plastic PCB clip to the motor terminals too.

You can now slowly pull the battery out of the battery holder. Be careful not to scrape the lower surface of the PCB with the positive tag as you might break a PCB track. It might help if you gently flex the PCB upwards slightly for clearance.

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Compare the original battery to its matching Li-ion replacement battery, available through ToothbrushBattery.com here. The groove around the body of the battery is at the positive end.

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Positive battery terminals:

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Negative battery terminals:

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The wire pins on the replacement battery need to be bent and shaped to fit the toothbrush. When bending the pins there is the risk of pulling the pins off the battery where they are welded on. Hold the pins with needle nose pliers close to the welded section then bend the pin around the pliers by hand.

Looking at the positive end of the replacement toothbrush battery, bend the wire pin 45 degrees to the left. Make sure the bend is just where the pin reaches the edge of the battery. Rotate the battery 45 degrees clockwise so the wire pin is pointing up vertically.

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At the negative end of the new battery bend the wire pin to the right by 135 degrees or more. The tighter the bend the better. Then at the edge of the battery bend the wire pin 90 degrees to the left so that it is parallel to the positive pin.

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Hook the positive pin of the battery into the gap between the PCB and the white plastic frame as shown below.

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Manoeuvre the positive pin right into the notch in the PCB next to the white plastic support.

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Hold the battery down onto the lower surface of its holder then cut the wire pin using miniature side cutters level with the top of the PCB.

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Gently flex the PCB upwards then rotate and slide the new battery into position without scraping the PCB. Bending the positive pin forwards slightly might give a little extra clearance.

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Bend the negative pin away from the circuit board so it cannot accidentally touch the PCB.

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Push the battery up fully against the white plastic stopper and bend the positive pin if necessary so that the pin is under its hole in the PCB.

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Melt the motor connection solder joints and lower the PCB back into place, ensuring the positive battery pin goes through its hole in the PCB. Solder the positive battery pin to the PCB.

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Slide the coil holder fully back on to the bottom end of the PCB. This will also push the negative battery pin against the edge of the PCB.

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Solder the two copper coil wires to the PCB.

Cut off the negative battery pin level with the top of the black plastic coil support.

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Using lead-free silver solder form a solder connection from the PCB to the negative battery pin.

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New Li-ion batteries are normally supplied partially charged so you can now test the battery. First plug in the charger then hold the toothbrush assembly over the peg on the charger. The LEDs should indicate charging has started. If it doesn’t light up check the solder connections.

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Holding the toothbrush securely, press the upper button on the PCB to switch on the toothbrush. It should light up and start running. Switch it off again.

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Clip the LED surround back onto the PCB.

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Check inside the handle casing for debris then gently slide the innards of the toothbrush back into the casing.

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Ensure that the plastic shaft surround has been fully pushed out of the casing.

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Put the spring back inside the coil.

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Clip the base cap back in to the toothbrush, hooking it in at the back first.

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Fit the ring back onto the plastic shaft surround making sure it is fully clipped into place. You can use a 10 or 11mm ring spanner or an old brush head to force it on. Heating the ring in hot water beforehand helps it clip on more easily.

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You now have a fully repaired Oral-B Genius/Smart toothbrush!

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Give your toothbrush a full charge then it’s ready to use.

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To recycle your old battery it is safest to pull the tags off with pliers first, then put sticky tape over at least one end. You can then take it to your local supermarket battery collection point or civic recycling facility.

Please leave any comments, questions or suggestions about this Braun Oral-B Type 3765 battery replacement guide on our dedicated blog post here.