My particular board doesn't have a battery or any of the charging/RAM backup components fitted. We didn't need any NVRAM for the original application so the production boards didn't have anything they didn't actually need. We didn't use the 8279 in the production version either, but for some reason this card did have one fitted. Perhaps it was a test unit - I forget as it was almost 30 years ago now.
One of the 'tricks' with business purchases through Maplin, back in the early 90s when (MPS was still part of the offering), was that you could speak to your 'rep' and order variations of standard kits if you bought them in any sort of quantity. We had a custom version of the kit with no battery or charging components, only two 24 pin DIL sockets (one for ROM and one 2K RAM) and no 8279.
Buying in twenty at a time, we made a significant saving without the unnecessary parts. I suspect the original shop-bought kit we bought in when I first played around with the Z80 is still hiding in a desk drawer at the old office somewhere. Either that or the battery rotted and it got thrown away
Mike