Refer Silicon Chip Magazine August 2009
The first versions of the battery zapper included a checker circuit. The Mk III battery zapper (KC-5479) has a separate checker circuit – and this is it. It checks the health of SLA batteries prior to charging or zapping with a simple LED condition indication of fair, poor, good etc.

Overlay PCB and electronic components
Case with machined and silk-screened front panel

Note: Kit Requires a 220uH ferrite check (LF1104) not included.