[McMurdo]

I've got one the same, just 2 batteries. I think they were sold through argos. Maybe the 4-cell version was reserved for more upmarket retailers!
I bought mine new and it was never modified, looks just like yours.

I think the base can also be exchanged for a deeper one to accomodate 2 non-rechargable PJ996 batteries. There are mouldings in the top bit to accept self tappers to hold the appropriate brass busbars and contacts in place.

PS My auntie has a version with 6V yuasa lead acid battery and a 1/4in jack plug charging arrangement, but the moulding is the same. In this case there's a sticker on it which says 'manufacturerd by Clulite' or someone like that. I changed its battery about 10 years ago. That one, being a 6V version, has the PJ996 busbars fitted, and flying leads soldered to those. Again it was like that from new.