This BMW 520i is a M reg (1994).The battery isn’t in the engine compartment nor in the back bonnet.Tried and failed to find where the battery is situated.

I have a old Mazda MX5 (99 model) and a BMW 3 series (2008 model).

The battery on the Mazda is flat out and I don’t have a Break down cover on it. Can I use my new bmw to jump-start the mazda? Or are the new bmw batteries not compatible with the jump cables, etc?

Thanks in advance