Can I keep a record of the units at my customers' sites?

Yes, in the asset register on the Unlimited plan, and in the free trial. Each split system, hot water unit or switchboard has its site, make, model, serials and warranty, its model's manuals, and every job that worked on it. Add one by photographing its nameplate, and the crew see the units on their job and record what they did.

See The asset register and Add an asset from a nameplate photo.