A.Senior editor David Frane
responds: The motor can’t distinguish
between power from a nicad battery and power from a
lithium-ion battery. And because cordless tools are
designed so they won’t accept incompatible
(wrong-voltage) battery packs, you’re safe
using any battery pack from the same manufacturer
that fits the tool.
The earliest lithium-ion batteries were not
backward-compatible with nicad battery tools, but
that’s changed over time. Three of the
major tool companies — DeWalt, Hitachi,
and Ridgid — now make 18-volt batteries
that are both forward- and backward-compatible.
Makita and Milwaukee 18-volt batteries, on the
other hand, are not forward- and
backward-compatible. When Makita began making
lithium-ion batteries, it changed from a post-mount
to a slide-mount design, which means that its
lithium-ion packs do not fit earlier tools.
Milwaukee had already adopted the slide mount for
its nicad tools, but its lithium-ion slide mount
has a different shape. DeWalt and Hitachi stayed
with post-style mounts when they went to
lithium-ion cells, while Ridgid uses the same slide
mount for both types of 18-volt batteries.
Most chargers are also backward-compatible with
older batteries, provided they have the same kind
of mount. Due to advances in battery circuitry,
however, chargers are not forward-compatible; the
charger that came with a nicad tool will not work
with lithium-ion batteries.