The non-SI unit einstein is not accepted for use with the SI and should be avoided.
Anyway, unit names are normally printed in upright type, and they are treated like ordinary nouns. Names of units are spelled with a lower-case initial in English, except in the beginning of a sentence when a capital initial is used. This also applies to unit names that are derived from a proper name of a person such as kelvin, newton, joule, pascal, watt, hertz, coulomb, volt, farad, ohm, siemens, weber, tesla, henry, and thus also einstein.
For SI units, it is only the unit name degree Celsius that contains a capital letter. In keeping with the rule, the unit degree begins with a lower-case d and the modifier Celsius begins with an upper-case C because it is a proper name.
However, in quantity names containing a person’s name, the person’s name is spelled with a capital initial, for example, the Einstein transition probability for spontaneous emission $A_{jk}$.
These writing rules are in accordance with following references: