What improvements were made in the Kestrel 5 series vs the Kestrel 4 series Meters?

Here are the major differences:

• LiNK wireless connectivity (Bluetooth Smart / BTLE)
  Robust, easy connectivity to both iOS and Android mobile devices as well as Windows and Mac computers. (Computers require optional Kestrel USB Dongle.)
• Kestrel LiNK for mobile
  Get real-time, right now, with remote data viewing on phones and tablets up to 100’ away. Kestrel LiNK also provides easy data export, threshold alerts and simple firmware updates. At this time there are apps for iOS (iPhone, iPAD) and Android smart phones & tablets
• USB Data Transfer Cable
  No longer needed is the cradle as the optical IR cable plugs directly into any 5 series meter. The Kestrel USB Data Transfer Cable is waterproof, lightweight and low profile. It packs away much easier than the older style 4 series USB data transfer cable.
• Intuitive user-interface
  Easy to use, icon-based interface with widely spaced keys makes the Kestrel easy to use in multiple languages.
• Corrosion-resistant battery compartment
  Batteries can be lethal to any electronic device. We have all been there. The battery compartment of the Kestrel 5 series meters has been isolated to reduce damage as a result of a leaky battery.
• Scratch resistant / breakage resistant window
  Rigid & Scratch resistant, the new polycarbonate lens with scratch-coating will help reduce damage to the display. We also offer a Kestrel Screen Protector in our store for added security.
• Dual color backlight
  Popular customer request! In the past, many of our customers wanted the Olive Drab or Desert Tan color but with a standard backlight. For nighttime operations, the NV or night vision preserving backlight is indispensable but it may be a little more difficult to see during bright daylight hours. For this reason, the user can easily switch between standard white backlight or NV backlight on any 5 series meter!
• Larger, higher contrast screen
  Another popular customer request from our customers! "I can read everything fine but can you make it a little bigger and make the characters stand out a little more?" The new Kestrel 5 series display is larger and has a higher resolution which makes fitting more on one screen attainable. Charting, graphing and text are easier to read which will keep eyestrain to a minimum even during bright daylight hours.
• More secure battery door
  Rather than on the bottom of the unit, the new Kestrel 5 series battery door is located on the back of the unit. It is much larger, uses a larger o-ring and is easily opened without tools. Also you will notice that the lanyard no longer attaches to the battery door hinge
• Battery
  Yet more popular customer requests! "I lost the shim to my Kestrel 4500". "AAA Batteries are harder to find in the field than AA." Since the (2) AAA batteries used with the Kestrel 4500 have been replaced by a single AA battery in the Kestrel 5500, the ever unpopular battery shim has been done away with. The Kestrel 5 series meters now work with an easily accessible single AA battery which requires no shim. "When it comes time to replace the included Energizer Ultimate Lithium battery, we strongly recommend lithium. Lithium batteries have a longer shelf life, last longer and are much less likely to leak.
• Colors
  The Kestrel colors have changed to go along with current needs. You will notice that the 5500 now comes in three colors. The NV designation has been removed since each 5 series meter now includes an easily switchable white / NV backlight.