BT6 is the Battery Checker.

Every home should have this unique electrical accessory on hand because it so versatile. Tests all AAA, AA, C, D, 9V and button batteries, whether general-purpose, alkaline or rechargeable. Portable battery, bulb & fuse tester is handy to have at home or the office. Simulated load test to check if battery will work in use. Use it to test all standard household and auto light bulbs, and fuses too. Dual scale allows testing and measuring battery voltage or capacity. Requires one 9V battery (not included).
Test fuse
Tests auto and household fuses
Test light bulb
Tests auto and household bulbs
Specifications

The batteries which can be tested are:
AA, HP16, MN2400, R03
AA, HP7, MN1500, UM3
C, HP11, MN1400, SP11, LR14, UM2
D, HP2, MN1300, SP2, R20,UM1
PP3, MN1604, 6F22, 006P
Test bulb and fuse
When the needle is in the green area, the measured component is good. When the needle is in the red area. the measured component is in open circuit.
Power:9V battery (6F22)
Dimensions(W×L×T):66×150×32 mm
Weight:160g (with battery)