According to Karcher, the difference between Karcher FC 5 and FC 5 Premium hard floor cleaners is that the FC 5 Premium is the upgrade version of FC 5, it has all the features of the FC 5, but with improved debris pickup, two extra rollers, different detergent, and a white color body.
Otherwise, they are the same.

Product info and things you may want to know before buying:

• These machines are designed for cleaning hard floors, not for use on carpet and area rugs.
• They are corded, have a 25-foot/7m power cord.
• They have clean water tank and waste water tank to separate clean and dirty water.
• They use two rotating microfiber rollers to mop all standard hard floors, including hardwood, laminate, stone, tile, vinyl floors, etc.
  The rollers are automatically wetted by the clean water when the machine is ON, they spin at the speed of 500 rpm, wipe and pick up dirty water, dust, small crumbs, pet hair, etc. And the built-in vacuum motor will then suction these dirty things off the rollers, collect them into the waste water tank.
  Thus, you always clean the floors with clean water.
• According to Karcher, the FC 5 uses up to 85% less water when compared to traditional mopping, meanwhile providing better cleaning performance. And the cleaned floors will dry in no more than two minutes.
• They come with a clean and storage station for storing and cleaning the device.
• The rollers can be detached and cleaned under running water or washing machine.
• The waste water tank can be cleaned in the dishwasher.
• There is no detergent tank. You will have to add detergent into clean water tank if you want to use detergent.

  Karcher customer support say that they allow you to add your own detergent, however, “Detergents containing bleach, ammonia, or other corrosive substances is
  not permitted for use in this machine. The use of non-approved detergents can damage the appliance and will void the warranty”.

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  You can also use only water without adding any detergent.

• There’s no heater. You can add cold or lukewarm tap water into the clean water tank.
• They do not steam.
• There is no solution release trigger, the water comes out automatically when it’s powered on.
• The color scheme is the only difference between the grey and yellow microfiber rollers.
• They are hard floor cleaners, not vacuum cleaners.
• Come with clean and storage station for cleaning and storing the machines.
• The handle does not fold for storage.
• The FC 5 is designed in Germany and assembled in Lithuania.
• Weighs 11.02lbs / 5kg (without cleaning liquids)
• Dimensions are 12.60″ x 10.63″ x 48.03″ / 320mm x 270mm x 1220mm
• Carry 3-year limited warranty.

Download Karcher FC 5/FC 5 premium manual to learn more:
https://s1.kaercher-media.com/documents/manuals/raw/000/BTA-5612773-000-07.pdf

The differences between the Karcher FC 3, FC 5, FC 7, FC 7 Premium cordless hard floor cleaners are as follows:
(the FC5 is discontinued.)

• Cleaning Rollers on the device
  The FC3 and FC5 have 2 rollers whereas the FC7 and FC7 Premium have 4 rollers.
• Run Time
  FC3 and FC5 runs up to approximately 20 minutes whereas the FC7 runs up to 45 minutes.
• Speeds
  The FC3 and FC5 have only one speed which is 500rpm whereas the FC7/FC7 Premium have 2 cleaning level settings that have the speeds of 450RPM and 490rpm and a boost mode which has the max speed of 530rpm.
• Mechanism
  The Karcher FC 5 Cordless hard floor cleaner has a suction motor which vacuums the dirty water off the back of the two rollers and into the waste water tank which located on the back of the machine.
  The FC3, FC7 and FC7 Premium Cordless hard floor cleaners do not have a vacuum motor, it uses a scraping method to remove dirty water off the back of the rollers and collects the water in the waste water tank which located at the bottom.
• Tank Capacity
  Both of them have dual tanks: a clean water tank and a dirty water tank. The tanks on the FC5, FC7, FC7 Premium are a bit larger, the clean water tank holds up to 13.5 oz, dirty water tank holds up to 6.8 oz. Whereas the FC 3 cordless clean water tank capacity is 12.2 oz and waste water tank capacity is 4.7 oz.
• Dirty Water Tank Removal
  The dirty water tank on the FC 5 cordless is the easiest to remove to empty. Whereas the FC 3 cordless dirty water tank is under the floor head cover, you will need to remove the cover to reach the dirty water tank. For FC7 and FC7 Premium, you will need to lift the device to detachable the dirty water tray and use both your hands to move it and then empty.
• Weight
  The FC5, FC7, FC Premium Cordless are heavier, they weigh approximately 9.6 pounds (without accessories and cleaning fluids) versus 5.3 pounds on the FC 3 Cordless.
• Dimensions (L x W x H)
  The FC 5 Cordless is a bit bulkier.
  The dimensions of FC 7/FC7 Premium Cordless are
  12.2″ x 9.1″ x 47.6″.
  The dimensions of FC 5 Cordless are
  12.6″ x 10.6″ x 48″.
  The dimensions of FC 3 Cordless are
  12″ x 8.9″ x 48″.
• Storage Station
  The storage docks of the two units are also a bit different.
  The FC 5, FC 7/FC 7 Premium Cordless storage station is not only for storing the machine and rollers, but also allows you to rinse the device with fresh water in the storage station when finished using. You place the FC 5 Cordless into storage station, fill storage station with water and turn on the unit to do the rinsing procedure.
  The FC 3 Cordless storage station on the other hand does not have the feature to rinse the device.
• Charger Cord Length
  The FC 5 Cordless charger cable length is 59.06 inches versus 70.87 inches on the FC 3 Cordless.
• Battery
  The FC7/FC7 Premium use 25.55V battery pack, FC 5 Cordless has 25.2V battery pack versus 7.2V on the FC 3 Cordless.

FC7 vs FC7 Premium
The difference between them is:
** The FC7 Premium has LED headlights whereas the FC7 does not have.
** The FC7 Premium has a white base whereas the one on FC7 is yellow.
** The FC7 Premium comes with an extra set of rollers which is designed for cleaning stone floor, whereas the FC7 comes with only one set of universal rollers which are white and yellow, the rollers on FC7 Premium are white and grey.
** Besides the 500ml universal hard floor detergent that the FC includes, the FC7 Premium also comes with an extra bottle of 30ml stone floor cleaner.

Similarities:

• Powered by lithium-ion battery.
• Have separate dirty water tank and clean water tank.
• No separate detergent tank.
• Have On/Off button on the handle.
• LED display to show battery level.
• Include storage station to store the unit in upright position.
• Include a bottle of detergent (RM 536) 16.9oz/500ml.
• Rollers can be detached to clean. You can clean the rollers under running water or wash them in washing machine.
• Carry 3-year limited warranty.

Some questions and answers:

• How long will it take to charge?
  Empty battery will take approximately 4 hours to charge.
• Is the battery replaceable?
  The battery is not detachable. You cannot buy a second battery to swap out the battery to extend the run time.
  Disconnecting the battery will invalidate the warranty.
• Is there a button for spraying solution?
  No. Only a On/Off button.
• What types of floors can these machines be used on?
  These units can be used to clean all sealed hard floor types including varnished parquet, enamelled tiles, linoleum, PVC, linoleum, tiled, stone, oiled and
  waxed parquet, laminate and all water resistant floor coverings.
• Can you use just plain water?
  Yes.
• Can you use vinegar with water?
  According to customer service, yes.
• Can you use your own cleaning solution?
  According to customer service, yes.
  However, “detergents containing bleach, ammonia, or other corrosive substances is not permitted for use in this machine”.

Download manuals to learn more:
Karcher FC 3 Cordless Floor Cleaner manual:
https://s1.kaercher-media.com/documents/manuals/raw/000/BTA-5652543-000-01.pdf

Karcher FC 5 Cordless Floor Cleaner manual:
https://s1.kaercher-media.com/documents/manuals/raw/000/BTA-5658979-000-01.pdf

Karcher FC 7 Cordless Floor Cleaner manual:
https://s1.kaercher-media.com/documents/manuals/raw/000/BTA-5734544-000-02.pdf