£5 for one cr123? Pack of 10 Panasonic on Amazon £12.75, £1.28 each free delivery.
How much you paying for a cr123?
You use a branded name?
£2 a battery seems fair to me but I’m no business man.
Either of these two models will be fine in the house. Personally I would go for the quad. If you are fitting detection in an outbuilding then go for a dual-tech.