I worked on 1 of the first BYD forklifters provided in Europe.
That one has allmost 13000 hours of workingtime in less then 4 years.
No issues with the battery what so ever.
In the last couple of years i have seen only minor problems with these battery's, mostly because costumer leaves contact on for weekend with only 15% SOC battery. Battery will discharge to much and charger will not start. With some tricks you can recover the battery without losing capacity. Try that with a Lead/Acid battery.