May contain traces of nut
As stated above, proper chargers are designed to charge each cell individually. Even very cheap chargers attempt this (but very badly - see https://hummy.tv/forum/threads/interesting-items.3945/page-59#post-111795). Repeatedly charging and discharging a stack of series-connected NiCd or NiMH cells gradually amplifies the slight variations in the capacity of each cell until one fails and takes out the whole stack. So what I was saying is to use a proper charging arrangement and don't just try to recharge the stack by forcing current into it.Are you saying that I should only charge 1 battery in each charger at a time?
Yes, I am well aware the capacity of an AAA is much less than an AA (much smaller volume to hold the active ingredients), but for the benefit of all those who thought I meant AA: try comparing the size of a C cell with an AA cell, and tell me how an adapter could be made to convert the latter into the former (without access to Tardis technology).*Also why AAA's in C adapters rather than AA's
There remains a question whether 6V is enough. If it was, surely Pure (or whoever) would have made it a four cell battery compartment? It's untidy, but technically I prefer the external 6-cell battery pack.
* This cart shows the dimension specifications for cells: https://www.powerstream.com/Size.htm. AA is 50mm long, C is 46 mm long. Yes, I know Maplin have AA-C adapters, but I assume that is an error and they are actually AAA-C adapters (either that or they hope the extra 4mm can be taken up by the contact spring in the battery compartment - if the cells are actually end-to-end, the combined length error will be 20mm and I find it very hard to believe this would fit).
It's a shame there appears to be no such thing as a 5/6 C - then six NiMH cells could be fitted in the length of five ordinary C cells. If you can find them anywhere, the tidiest solution would be to source 1/2 or 2/3 C NiMH cells (the fraction refers to their length compared to the standard C length), and put six in the battery compartment with a spacer to make use the remaining length. Spacers would also be needed to fit them in the charger.