Summary of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2019

Schedule of computation of potentially dilutive securities

The following shares underlying outstanding convertible notes, stock options, RSUs and warrants to purchase common stock were antidilutive due to a net loss in the periods presented and, therefore, were excluded from the dilutive securities computation for the three months ended March 31, as indicated below.



	Three months ended March 31,
Excluded potentially dilutive securities (1):	2019	2018

Convertible note - principal	—	702,247
Options to purchase common stock	3,440,437	561,536
Unvested restricted stock units	244,785	63,600
Financing warrants to purchase common stock	2,444,328	2,340,828
Total potential dilutive securities	6,129,550	3,668,211


(1)	The number of shares is based on the maximum number of shares issuable on exercise or conversion of the related securities as of the period end. Such amounts have not been adjusted for the treasury stock method or weighted average outstanding calculations as required if the securities were dilutive.

Schedule of concentration of credit risk

Revenues from the following customers each represented at least 10% of total revenue for the three months ended March 31, 2019 and 2018, respectively. They also represented a significant portion of our accounts receivable as of March 31, 2019 and December 31, 2018, respectively.



	Revenue				Accounts Receivable
	Three months ended March 31,				March 31, 2019		December 31, 2018
	2019		2018		March 31, 2019		December 31, 2018

Clarios (successor of Johnson Controls Battery Group, Inc.)	60	%	79	%	60	%	95	%
Ocean Partners USA, Inc.	—	%	18	%	—	%	—	%
P. Kay Metals	37	%	—	%	37	%	—	%