linear mixed model using lmer

Dear all, I have this simple dataset to measure the yeild of a crop collected in 2 batches (attached). when I ran a simple inear mixed model using lmer to estimate within-batch and between-batch variability, the between-batch variability is 0. The run showed that data is singular. Does anyone know why the data is singular and what's the reason for 0 variability? is it because the dataset only has 2 batches?

daty<-read.table("datx.txt",sep='\t',header=T,row.names=NULL)
library(lme4)> lmer(yield~1+(1|batch),daty)

boundary (singular) fit: see ?isSingular
Linear mixed model fit by REML ['lmerMod']
Formula: yield ~ 1 + (1 | batch)
? ?Data: daty
REML criterion at convergence: 115.6358
Random effects:
?Groups? ?Name? ? ? ? Std.Dev.
?batch? ? (Intercept) 0.000? ?
?Residual? ? ? ? ? ? ?2.789? ?
Number of obs: 24, groups:? batch, 2
Fixed Effects:
(Intercept)??
? ? ? 5.788??

Thanks!
John