Prepare for and practice interview questions from Enersys.

Enersys Interview Questions

Enersys Interview Guides

Data Structures & Algorithms

Given an integer N, write a function that returns all of the prime numbers up to N

Prime to N

This problem involves identifying duplicate numbers in a list of integers. The function should return a list of the duplicate numbers.

Find Duplicate Numbers in a List

Write a function that tests whether a string of brackets is balanced.

The Brackets Problem

Machine Learning

Let's say that you're training a classification model.   How would you combat overfitting when building tree-based models?

Overfit Avoidance

How would you investigate the cause of this training instability?

Training Instability in Neural Networks

Brainteasers

How would you answer when an Interviewer asks why you applied to their company?

Why Do You Want to Work With Us

What do you tell an interviewer when they ask you what your strengths and weaknesses are?

Your Strengths and Weaknesses

Data Pipelines

Describing a real-world data cleaning and organization project

Data Cleaning Experiences

Design Patterns

Create a text editor while displaying method overriding as a concept.

Text Editor With OOP

When an interviewer asks you a question along the lines of:

<ul>
<li>Why did you apply to our company?</li>
<li>What are you looking for in your next job?</li>
<li>What makes you a good fit for our company?</li>
</ul>

How should you respond?

When asked 'What are you looking for in your next job?' in an interview, how can you tie the company's employee benefits into your response?

When asked 'What are you looking for in your next job?' in an interview, how can you tie the company's employee benefits into your response?

Why Do You Want to Work With Us I

How can company values be used effectively in an interview when asked 'What makes you a good fit for our company?'

How can company values be used effectively in an interview when asked 'What makes you a good fit for our company?'

Why Do You Want to Work With Us II

When responding to the question 'Why did you apply to our company?' during an interview, what aspect should you highlight?

When responding to the question 'Why did you apply to our company?' during an interview, what aspect should you highlight?

Why Do You Want to Work With Us III

When an interviewer asks a question along the lines of:

<ul>
<li>What would your current manager say about you? What constructive criticisms might he give?</li>
<li>What are your three biggest strengths and weaknesses you have identified in yourself?</li>
</ul>

How would you respond?

When asked about your strengths in an interview, what is an effective way to respond?

When asked about your strengths in an interview, what is an effective way to respond?

Your Strengths and Weaknesses I

Which of the following is an acceptable strategy when discussing weaknesses in an interview?

Which of the following is an acceptable strategy when discussing weaknesses in an interview?

Your Strengths and Weaknesses II

Describe a data project you worked on. What were some of the challenges you faced?

Describing a data project and its challenges

Hurdles In Data Projects

Analytics

Let’s say that you’re training a classification model.

How would you combat overfitting when building tree-based models?

Tell me about a project in which you had to clean and organize a large dataset.

Given an integer <code>N</code>, write a function that returns a list of all of the prime numbers up to <code>N</code>.

Note: Return an empty list there are no prime numbers less than or equal to <code>N</code>.

Example:

Input:

<pre tabindex="0" class="chroma"><code>N = 3
</code></pre>

Output:

<pre tabindex="0" class="chroma"><code>def prime_numbers(N) -&gt; [2,3]
</code></pre>

You’re given a string that may contain the characters <code>{</code>, <code>}</code>, <code>[</code>, <code>]</code>, <code>(</code>, and <code>)</code>.

Task: Verify that the string is balanced. A balanced string is one where every opening character, <code>{</code>, <code>[</code>, or <code>(</code>, has a corresponding closing character, <code>}</code>, <code>]</code>, or <code>)</code>.

Write a function called <code>is_balanced(string: str) -&gt; bool</code> which verifies the balance of a string.

Example:

<pre tabindex="0" class="chroma"><code>is_balanced(&#39;(())[]{}&#39;) -&gt; True
</code></pre>

<pre tabindex="0" class="chroma"><code>is_balanced(&#39;{([(){}])()}&#39;) -&gt; True
</code></pre>

<pre tabindex="0" class="chroma"><code>is_balanced(&#39;{}[]())&#39;) -&gt; False
</code></pre>

<hr/>

Given a list of integers, identify all the duplicate values in the list. Assume that the list can contain both positive and negative numbers, and the order of the list does not matter. A number is considered a duplicate if it appears more than once in the list. Return a list of the duplicate numbers.

Example 1:

Input:

<pre tabindex="0" class="chroma"><code>nums = [1, 2, 3, 1, 2, 3]
</code></pre>

Output:

<pre tabindex="0" class="chroma"><code>find_duplicates(nums) -&gt; [1, 2, 3]
</code></pre>

The numbers 1, 2, and 3 all appear more than once in the list, so they are considered duplicates.

Example 2:

Input:

<pre tabindex="0" class="chroma"><code>nums = [1, -1, 2, 3, 3, -1]
</code></pre>

Output:

<pre tabindex="0" class="chroma"><code>find_duplicates(nums) -&gt; [-1, 3]
</code></pre>

The numbers -1 and 3 both appear more than once in the list, so they are considered duplicates. Note that the order of the output does not matter.

Example 3:

Input:

<pre tabindex="0" class="chroma"><code>nums = [1, 2, 3, 4, 5]
</code></pre>

Output:

<pre tabindex="0" class="chroma"><code>find_duplicates(nums) -&gt; []
</code></pre>

None of the numbers in the list appear more than once, so there are no duplicates.

You have been tasked with designing three classes: <code>text_editor</code>, <code>moving_text_editor</code>, and <code>smart_text_editor</code>. These classes are to be created with specific functionalities as defined below:

<ol>
<li><code>text_editor</code> class:

<ul>
<li><code>write_line(string:str)</code>: A method which appends a given string to the end of the existing string.</li>
<li><code>delete_line(char_num : int)</code>: A method which deletes <code>char_num</code> number of characters from the existing string, starting from the end. If there are no characters left, the method should do nothing.</li>
<li><code>special_operation()</code>: A method which currently does nothing.</li>
<li><code>get_notes()</code>: A method which returns the internal string.</li>
</ul></li>

<li><code>moving_text_editor</code> class:

<ul>
<li>This class extends <code>text_editor</code>. The <code>special_operation()</code> method is overridden. Initially, the cursor will be at the end of the current string. If <code>special_operation()</code> is called, it moves the cursor to the beginning of the string, any additional appends will be appended to the beginning of the string instead. Calling <code>special_operation()</code> again reverses the cursor operation.</li>
</ul></li>

<li><code>smart_text_editor</code> class:

<ul>
<li>This class extends <code>text_editor</code>. In this class, the <code>special_operation()</code> method is overridden to serve as an undo operation, allowing it to undo an infinite number of operations.</li>
</ul></li>
</ol>

<h3>Input</h3>

<pre tabindex="0" class="chroma"><code>[[&#39;special_text_editor&#39;], [&#39;write_line&#39;, &#39;special_operation&#39;, &#39;write_line&#39;], [&#39;World&#39;, &#39;Hello, &#39;]]
</code></pre>

<h3>Output</h3>

<code>&#34;Hello, World&#34;</code>

You’re AI engineer working on an energy forecasting system at Siemens that helps utilities predict short-term electricity demand to balance grid load and reduce outages. You train a recurrent neural network on long historical time series (weather, calendar effects, local demand signals) to forecast energy demand.

Early in training, the model appears to learn normally, but after several epochs the loss becomes highly unstable, oscillating wildly before turning into NaNs. At the same time, training slows dramatically and the model fails to recover even after restarting from recent checkpoints.

You’ve verified that the data pipeline is correct and labels are well-aligned with inputs. No changes were made to the dataset, but increasing the sequence length or learning rate makes the problem significantly worse.

How would you investigate the cause of this training instability? What signals would you look for during debugging, and how would those findings guide the changes you make to the model or training setup?

Let’s say we have a search form in our web app where users can enter a keyword like “star”, and the system searches for matches across several different fields in a large database table. Lately, these searches have been timing out when users search for common words.

How would you approach diagnosing and resolving these search timeouts?

How would you resolve slow, timing-out keyword searches across multiple database fields?

Search Timeout

Query Optimization

Let’s say we’re managing a production line for assembling electric scooters, with 10 stations where each has a different average processing time per unit (for example, Station 1 takes 5 minutes, Station 2 takes 3 minutes, and so on).

How would you determine the right metric to use for balancing worker allocation across the stations, and how would you use it to figure out how many workers each station needs?

How would you decide on a metric and approach for worker allocation across an uneven production line?

Worker Distribution Dilemma

Supply Chain

Challenge

<div><h2>PMO Finance Intern</h2>EnerSys is a global leader in stored energy solutions for industrial applications. We have over thirty manufacturing and assembly plants worldwide servicing over 10,000 customers in more than 100 countries. Worldwide headquarters are located in Reading, PA, USA with regional headquarters in Europe and Asia. We complement our extensive line of Motive Power and Energy Systems with a full range of integrated services and systems. With sales and service locations throughout the world, and over 100 years of battery experience, EnerSys is the power/full solution for stored DC power products.<h2>Job Purpose</h2>The PMO Finance Intern is an entry-level, developmental role within the Project Management Office (PMO), supporting financial tracking, analysis, and reporting across active projects and the broader project portfolio. This role provides hands-on exposure to project financial management, cost controls, forecasting, and governance while reinforcing the execution discipline that defines a high-performing PMO. The intern partners closely with Project Managers, PMO leadership, and Finance to ensure accurate financial data, timely reporting, and adherence to PMO standards. This position is designed to build foundational skills in project financials, analytical thinking, and professional accountability, serving as a pipeline into future PMO or Finance roles.<h2>Essential Duties and Responsibilities</h2><ul><li>Support project financial tracking, including budgets, actuals, forecasts, and variance analysis across assigned projects.</li><li>Assist Project Managers in maintaining accurate cost data within PMO systems (e.g., Planisware, Excel, or other approved tools).</li><li>Help prepare monthly and ad hoc financial reports, dashboards, and summaries for PMO leadership review.</li><li>Track purchase orders, invoices, and accruals in coordination with Finance and project teams.</li><li>Support portfolio-level financial analysis, including trend identification and data validation.</li><li>Participate in project reviews and PMO governance meetings to gain exposure to decision-making and financial controls.</li><li>Maintain organized and auditable financial documentation aligned with PMO process requirements.</li><li>Assist with lessons-learned activities and continuous improvement initiatives related to cost management and reporting.</li><li>Demonstrate professionalism, accuracy, and attention to detail in all deliverables.</li><li>Embody the PMO's "Hungry and Humble" mindset eager to learn, receptive to feedback, and committed to team success.</li></ul><h2>Qualifications</h2><ul><li>Currently pursuing a Bachelor's degree in Finance, Accounting, Business, Engineering, or a related field.</li><li>Strong interest in project financial management, analytics, or PMO operations.</li><li>Proficiency with Microsoft Excel; experience with data analysis or reporting tools is a plus.</li><li>Strong attention to detail and ability to manage multiple tasks with accuracy.</li><li>Clear written and verbal communication skills.</li><li>Demonstrated reliability, curiosity, and willingness to learn in a professional environment.</li></ul><h2>General Job Requirements</h2><ul><li>This position will work in an office setting, expect minimal physical demands.</li></ul></div>

Calculate Moving Average	SQL	Easy
Predict Customer Churn	Machine Learning	Medium
A/B Test Significance	Statistics	Medium
Optimize Query Performance	SQL	Hard
Feature Importance Analysis	Machine Learning	Medium
Clean Missing Data	Python	Easy
Neural Network Architecture	Deep Learning	Hard
Calculate Cohort Retention	SQL	Medium
Bayesian Probability	Statistics	Easy
Recommend Similar Products	Machine Learning	Hard

Enersys Interview Questions

Enersys Interview Guides

Enersys Interview Questions

Challenge

Enersys Opening Jobs

Discussion & Interview Experiences

Discussion & Interview Experiences