Fish, or Silver-Fish Batteries, are made to slide down behind the saddle, into a vertical cavity behind the seat tube. Normally the controller is mounted in a cavity directly below the battery. 

These batteries were fairly popular on 'economy' ebikes built between 2010 and 2020.  Many of these batteries will now be due for replacement, and the good news is that we can now provide better quality cells, giving longer lifespans, and for considerably less weight per Wh.

These batteries come complete with charger, mounting plate and rear slide rail (in case it doesn't fit perfectly on your existing slide bracket).

• 36v 17.5ah (630 watt hours)
• LG 3500mAh cells, 18650 type
• Weight 3.5kg (brackets excluded), or 2.5kg for 10.5ah version (same case)
• Dimensions 380 x 110 x 80mm