Hawker batteries. They are a alternative to Dynabatt batteries. The 2 types of Hawkers I have seen people use are the Ge or Gp 13 (11lbs) and the G16ep (13 lbs, same as the Dynabatt). I have had the G16 for about a year now, only had to jump it once after it sat for Dec and Jan.

The series letters may be off a little but the 13 and 16 I am pretty sure about.