After a fair amount of time researching NiMh batteries and the various types of battery charger available on the web, I have finally bought some 'D' type rechargeable batteries and a couple of chargers.
Initially I was looking at a number of 'D' type batteries available from a well known auction site, unfortunately a lot of the brands that were being auctioned I had not heard of, and Googling a number of the brands brought no results. I did contact one vendor to ask him who manufactured the batteries he was selling, he was very honest and told me that he had no idea as he only bought and sold items.
I was further alarmed by a story I came across on the web concerning a company who had been using an 'AA' battery which was then encased in a 'D' type shell. The author of this article who also published photos of the offending battery advised buyers of 'D' type batteries to weigh them to make sure they were buying the genuine article!
There are some decent batteries available on auction sites but one has to do a fair amount of homework to make sure you are buying a decent product, this time around I decided to buy batteries and chargers that were well known brands.
For 'D' type batteries I purchased the AccuPower Universal Charger - AccuManager20 - which accepts AAA, AA, C, D and 9V 'in any combination at the same time'. I also purchased six AccuPower 11500 'Digital Power' D type batteries.
Charging 'D' type batteries can take a fair amount of time, the charger is fully automatic in operation and it decides how long to charge each battery, for example the battery in Channel 1: took 19hours - 18mins to be fully charged and the others took Channel 2: 19hours - 54min, Channel 3: 16hours - 56mins and Channel 4: 16hours. Then of course I had to charge the remaining two batteries! I might consider buying a further Universal charger so that all batteries can be charged at the same time.
Due to the length of time charging the 'D' type batteries I then went and purchased a La Crosse Technology Model: BC-1000 charger for my AAA and AA batteries, I chose this model as it came with a case and various batteries and it was on special offer!
Reading the Roberts Stream 205 manual it states that "If using batteries only alkaline types should normally be used. Battery life will vary according to the use of the radio, but between 40 and 80 hours should be possible. WiFi use takes much more power than DAB listening, for example."
They do mention NiMh batteries but mention that 'commercially' available batteries will only power the radio for a few hours before needing recharging.
I put the AccuPower 11500 batteries in the radio and monitored my listening times to gauge how long the batteries lasted before expiring.
As WiFi Internet radio takes the greatest amount of power I decided only to use that medium for my test and ignored DAB and FM, listening only to Internet radio I managed to get 26hours - 30mins out of the batteries before they required recharging. A mixture of FM/DAB/Internet radio listening would improve on that figure and of course just listening to FM would give the best return.
At a later date might try some of the batteries from the auction site to see how they perform although I might just buy a sample battery so that I can weigh it to see whether its a genuine 'D' type battery!