This guide will take you through how to open the Waterpik WP-450 cordless water flosser and repair it by replacing the internal rechargeable battery. For details on other parts such as motors, tips and chargers see our Waterpik Spare Parts page.
The disassembly and repair tutorial is based on the Waterpik WP-450 flosser model shown above but is also applicable to other cordless Waterpik models such as the WP-440, WP-450A, WP-450C, WP-450E, WP-450EU, WP-450UK, WP-455, WP-460, WP-461, WP-462, WP-463, WP-464, WP-465, WP-466 and the WP-470 models. The WP-360 Waterpik models were made with two different types of battery pack, so you might be able to repair your WP-360 if it is the later version fitted with the same side-by-side type of battery pack shown here. The model number of your Waterpik flosser is marked on a label on the bottom of the flosser or on the back of the Waterpik behind the water reservoir.
The basic method is:
- Open and dismantle your Waterpik flosser
- De-solder the old rechargeable battery
- Solder in the replacement battery
- Reassemble the Waterpik and recharge the new battery
This is documented in detail below along with lots of pictures.
Any damage to yourself, your device or anything else is entirely your responsibility. This guide is for professional, educational purposes only and is offered without guarantee or liability.
We have created a short video from this guide to Waterpik WP-450 water flosser battery replacement on our YouTube channel, which you can also watch below.
Tools / Parts / Equipment
- Waterpik WP-450 water flosser
- Compatible charger
- Soldering iron: Electronics grade (about 18-25 watt)
- Solder: Lead-free silver solder is great for this
- Solder sucker (also known as a desoldering pump) and/or desoldering braid
- Small cross-head screwdriver e.g. Phillips no. 1
- Large flat-bladed screwdriver: 5 to 8mm wide
- Temporary tape
- Scrap of cardboard
- Optional double-sided tape
- Replacement 2.4V Ni-MH battery with solder tags. Support us by buying from Ionic Industries here. Other designs of Waterpik battery are described here.
To start with, empty the water reservoir of your water flosser. Then release the clip underneath and slide the reservoir downwards and off the bottom of your Waterpik. Also remove the nozzle/jet/tip from the top.
(Click on any picture to enlarge it.)
Temporarily tape a piece of cardboard to the top of the Waterpik to protect it from getting scratched.
Using a large, flat-bladed screwdriver resting on the cardboard gently pry the nozzle holder out of the body of the Waterpik. Make sure it doesn’t fly off across the room!
The removed piece:
Using a small cross-head (phillips) screwdriver remove the 4 screws from the back of the flosser arrowed below.
Lift up and unhook the back cover to remove it.
Remove the 2 screws holding the inner plate.
Start to pry up the inner plate that carries the pipework.
Turn over the Waterpik and check that the charging socket is coming away with the inner plate and isn’t stuck to the front of the flosser.
Continue to lift the inner plate and move it slightly to the right.
Gently pull the inner plate away from the top of the flosser while twisting it slightly anti-clockwise to disengage the nozzle release mechanism from the blue nozzle release button (arrowed below).
Continue to twist and remove the inner plate until it is free from the body of the Waterpik. Don’t lose the blue nozzle release button!
Turn over the inner plate to see the motor and battery.
Note how this battery is right at the bottom of its compartment with a gap at the top. You will need to re-fit your new battery in a similar location to your original battery to ensure that the wires can reach the solder tags on the new battery.
Note how the wires pass through cutouts in the battery retaining clamp.
Remove the battery retaining clamp and note the polarity of the battery and its wires. The red wire goes to the positive battery terminal.
Time to get your soldering iron warmed up now! Using the soldering iron and a desoldering pump or some desoldering braid first desolder the black motor wire from the negative battery terminal. You might need to cut the wire where it is soldered to the battery tag if you have one continuous wire from the motor to the battery to the charging socket.
Desolder the wire from the charging socket where it is soldered to the negative battery tag.
Desolder the two wires from the positive battery tag. The black ‘wire’ in this photo is actually a sleeved electronic component – probably a diode to prevent damage in case the charger is somehow connected with reverse polarity.
Pry the original battery out of its compartment. This one was held in with some weak glue.
Compare the original battery to its replacement. Please support our writing of these repair guides by buying your new battery from Ionic Industries here. Your original battery will be 2.4V and will probably have a capacity of between 1300mAh and 1500mAh. This can be safely upgraded to our 1800mAh 2.4V pack to give you a longer running time between recharges.
Note: Some older versions of the WP-450 were fitted with a single cylindrical battery pack made up of two short 1.2V cells joined end to end. If yours is one of these please see the battery section on our Waterpik parts page for details on replacing these discontinued batteries.
Note the relative positions of the positive battery terminals arrowed below. They are in opposite locations. On the left side of the original battery pack and on the right side of the new replacement battery pack.
We can easily reverse the polarity of the new battery pack by folding the solder tags back on themselves. First, fold the tags outwards.
Turn the battery pack over.
Fold the tags upright, then slightly towards the back of the pack.
Trim the solder tags to a similar length as the tags on the original battery pack. You can leave them slightly longer for a bit of flexibility in fitting if required.
Test the fitment of the new battery and that the wires reach the solder tags. Once you’re happy with its position you can use a little double-sided tape to hold it in place. This is not essential as the retaining clamp will hold it in place later.
Tin the two solder tags with solder, making sure that you do not melt the plastic sleeving of the battery cells as this could cause a short circuit.
Solder the 4 wires to the new battery’s solder tags. Again, make sure you don’t melt the plastic of the battery.
Re-fit the battery retaining clamp, making sure that the wires pass through the slots in the clamp.
Re-fit the nozzle release button in the flosser’s casing and temporarily tape it into place so it doesn’t fall out.
Check that the power switch is still off and that the speed selector switch is still in the position that matches the lever on the inner panel (both down in the photos below).
Hook the inner plate into the Waterpik’s casing at an angle so it goes behind the screw towers. First on the left side:
Then on the right side:
Manoeuvre the inner plate it so that the blue nozzle release button connects with the release mechanism correctly (arrowed).
Remove the tape from the nozzle release button and check that it can be pressed in and springs out.
The inner plate can be pushed fully into place.
Check that the speed selector switch has engaged and moves the internal lever correctly.
While holding the inner plate into the casing by hand you can now lift up the whole Waterpik assembly and check that the power switch works by switching it on for a second or two. There should be enough charge in the new battery to run the motor a little.
Check that the charging socket is flush with the front of the flosser housing.
Re-fit the 2 screws that hold the inner plate in place. These are self-tapping screws so to avoid cross-threading them drop each one into its hole then, before tightening each one, first give it half a turn or so anti-clockwise until they ‘click’ and drop into their thread.
Re-fit the 4 screws that hold the back cover in place.
Clip the nozzle holder back into place.
Check that the motor still runs then plug your Waterpik flosser in to charge for a full 24 hours.
You now have a fully repaired Waterpik water flosser! We’d love to hear about your Waterpik repair experience so please leave any questions, hints or tips in the comments section below.
Notes on Charging
The original charger supplied with the Waterpik flosser shown above is rated with an output current of 100mA. To fully charge the higher capacity 1800mAh battery from empty this will take 18 hours, plus the recommended additional 50% to compensate for losses (an extra 9 hours). This takes it up to 27 hours of charging for a full slow charge using the original Waterpik charger. Check your own charger to see if it is rated at a different output current.