My choice of batteries is MK as I have found that they last much longer than any other brand, I frequently find MK batteries over 4 years old and up to 17 years old! Whilst the initial cost may be a little bit more they will last at least 1 or 2 times as long as cheaper batteries so an extra few pounds spent at the beginning can save you hundreds later on.
MK Battery provides the highest quality and most environmentally responsible sealed battery solutions for specialized deep-cycle applications. Advanced design and manufacturing make MK sealed VRLA and Gel batteries the standard by which all other batteries are measured.
We then get into should you have AGM or Gel batteries. It will depend on what your use is, for someone that uses a scooter or chair daily for long periods then GEL are the best option. For those who use it occasionally then AGM are perfect.
PLEASE NOTE: This is just a brief breakdown of batteries, should you need new batteries I will discuss with you all of the options and work out what is best for you, not what is best for me! When I worked for a large mobility company their policy was fit GEL to everything, not because they are the best for every customer, it was because they made more profit on them.