A 12 volt battery, when fully charged, should register about 13,5 volts off load, and not much less than 12 volts when on load.
Ibhetri eneshumi elinesibini womlinganiselo wamandla ombane, xa igcwele, mayibonise ishunci elinesithathu nesiqingatha zomlinganiselo wamandla ombane xa isisiwe, kwaye ingaphantsi kweshumi elinambini zomlinganiselo wamandla ombane xa ifakiwe.