Thanks for taking the time to reply.
Jack: it's news to me that you have to 'tamper' with a battery's casing to have it work!
Again, no mention of this in the instruction booklet - and since the batteries have performed perfectly up till recently, it's unlikely to be a factor.
You mention you replaced the originals - but not if you'd done so with the same or higher capacity ones (I'm asssuming 'rechargeable' ones?)
Did the Lidl headphones come with 500 or above and did you replace with the same or higher capacity? I'd be interested in knowing.
Wilham: the charging device (also an excellent buy from Aldi)I've had for a few months and it charges perfectly (LED's control from 'red' to 'green' and don't allow 'over-charge') So I doubt if it's the charger.
Besides, I've two different battery testers and they show exactly the same level of full charge when a my Aldi (and other)batteries are checked after full recharge. So, the charger itself seems to be doing its job.
The main point remains: why aren't the higher capacity Maplin ones working in the Aldi unit?
Any other ideas?