I've got a clone of a Makita BL1830 (so a differently-shaped 18V Li+ battery) as well as one of the genuine article. Subjectively the only difference is that the clone is a bit sloppy with the physical tolerances, so is a bit stiffer at sliding into the tools/charger. I haven't attempted to measure the capacity, thoguh.
Update:
While the capacity seemed adequate, the inherent shoddiness became apparent when, after an afternoon of enthusiastic hole-sawing a couple of years ago, it refused to charge.
Opening it up revealed a complete absence of cell-balancing circuitry, and a several of cheap-looking cardboard cells that were b0rked beyond hope. I re-configured the remaining good cells as a battery of half the capacity, charged them individually with the bench supply, and got a little more use out of it before they too succumbed.
I replaced it with an official Makita battery, as the original one from 2014 was still fine. Internet research has informed me that they balance the cells properly, but suffer from an overly paranoid design feature whereby the battery management circuit intentionally bricks itself after three failed charges. One common cause of failed charges is if the cells that are tapped to power the battery management are allowed to completely discharge (ie. by a discharged battery being left lying around for months).
The take-home lesson being that if you have an official Makita battery:
a) Make sure it isn't allowed to completely self-discharge
b) If it fails to charge in the official charger, don't just try again, open it up, check the individual cell voltages, and if necessary recharge them directly before letting it anywhere near the official charger again
Alternatively, if you use third-party batteries, some sort of bodgery to balance the cells will make them last longer.