How to force biblatex to typeset doi in lower case (with a period replacing the colon after the word 'doi')

Question

I am using the biblatex-ieee package, i.e. the biblatex package with the ieee style loaded.

In my bibliography, I wish to do two things that the package doesn't currently do.

1. Replace the colon after the word DOI with a period
2. Typeset the word "DOI" and the actual DOI in lowercase (presently they are in smallcaps)

How can I achieve this? Here's a MWE:

\documentclass{article}
\usepackage[style=ieee]{biblatex}
\begin{filecontents*}{example.bib}
@article{Ahmed2014,
author = {Ahmed, Ryan and {El Sayed}, Mohammed and Arasaratnam, Ienkaran and {Jimi Tjong} and Habibi, Saeid},
doi = {10.1109/JESTPE.2014.2331059},
file = {::},
issn = {2168-6777},
journal = {IEEE Journal of Emerging and Selected Topics in Power Electronics},
month = {sep},
number = {3},
pages = {659--677},
title = {{Reduced-Order Electrochemical Model Parameters Identification and SOC Estimation for Healthy and Aged Li-Ion Batteries Part I: Parameterization Model Development for Healthy Batteries}},
url = {http://ieeexplore.ieee.org/document/6838950/},
volume = {2},
year = {2014}
}
\end{filecontents*}
\addbibresource{example.bib}

\begin{document}
Hello
\nocite{*}
\printbibliography
\end{document}

Answer 1

The DOI formatting is controlled by DOI field format defined in biblatex.def. We just need to redefine it from

\DeclareFieldFormat{doi}{%
  \mkbibacro{DOI}\addcolon\space
  \ifhyperref
    {\href{https://doi.org/#1}{\nolinkurl{#1}}}
    {\nolinkurl{#1}}}

to something we want. Instead of redefining the \mkbibarco, I just stick the text in, replace \addcolon with \adddot and add a few \lowercase to get

\DeclareFieldFormat{doi}{%
  doi\adddot\space
  \ifhyperref
    {\lowercase{\href{https://doi.org/#1}{\nolinkurl{#1}}}}
    {\lowercase{\nolinkurl{#1}}}}

Putting it all together

\documentclass{article}
\usepackage[style=ieee]{biblatex}

\DeclareFieldFormat{doi}{%
  doi\adddot\space
  \ifhyperref
    {\lowercase{\href{https://doi.org/#1}{\nolinkurl{#1}}}}
    {\lowercase{\nolinkurl{#1}}}}


\begin{filecontents*}{example.bib}
@article{Ahmed2014,
author = {Ahmed, Ryan and {El Sayed}, Mohammed and Arasaratnam, Ienkaran and {Jimi Tjong} and Habibi, Saeid},
doi = {10.1109/JESTPE.2014.2331059},
file = {::},
issn = {2168-6777},
journal = {IEEE Journal of Emerging and Selected Topics in Power Electronics},
month = {sep},
number = {3},
pages = {659--677},
title = {{Reduced-Order Electrochemical Model Parameters Identification and SOC Estimation for Healthy and Aged Li-Ion Batteries Part I: Parameterization Model Development for Healthy Batteries}},
url = {http://ieeexplore.ieee.org/document/6838950/},
volume = {2},
year = {2014}
}
\end{filecontents*}
\addbibresource{example.bib}

\begin{document}
Hello
\nocite{*}
\printbibliography
\end{document}