Not to answer your question, but buy a vacuum with a decent length power cable (Numatic or Sebo) and your battery issues are gone, you'll also find a corded cleaner does a much better job.
A Numatic or Sebo will also be bagged, so no messy bagless container to empty or filters to constantly wash. Plus, a Numatic or Sebo will outlast any Hoover/Vax/Dyson/Shark and are easily repairable if they do go wrong with easy parts availability.
It's horses for courses. I have a corded Henry (Numatic) and two cordless Gtechs (handheld and upright).*
The Henry comes out a few times a year when I'm doing a "proper" clean, moving furniture etc. and taking an hour or more. The cordless ones come out several times a week, but just for a few minutes at a time, to deal with dirt I've just noticed, or brought in from the garden, or similar.
More on-topic, both the Gtechs are around five years old or more, and both their original batteries seem to be doing okay so far. They get charged about once a month or six weeks.
(* I'm not as much of a cleaning fan as this may suggest, as I inherited two of them.)
