Each cordless power tool battery type requires specific conditions in order to charge efficiently without damaging the battery cells. Chargers are available to cater for each chemistry and some can automatically adjust their settings to accommodate multiple chemistries and conditions.
The main differences between chargers, apart from chemistry, include the current and voltage levels used and how the charger determines that the battery is charged. The best chargers are called ‘smart chargers’ because they have a microprocessor (computer chip or microchip) which monitors the condition of the battery and adjusts itself accordingly.
NiCd battery chargers
Ideally, NiCd battery chargers use a very fast charge during the bulk stage of charging (see {{widget type=”cms/widget_page_link” anchor_text=”How does a cordless power tool battery charger work?” title=”How does a cordless power tool battery charger work?” template=”cms/widget/link/link_inline.phtml” page_id=”4031″}}) or a very slow charge throughout the charging process. A slow charge takes a lot longer so is not always suitable.
The best chargers have a microprocessor which monitors when the voltage drops, a reliable sign that the battery is fully charged.
Some NiCd battery chargers swap between charging the battery to discharging it for short bursts. This is known as ‘burp’ or ‘reverse load’ charging. This process encourages the battery to accept more charge, speeding up the process and preventing overheating. It can reduce memory affect, increase service life and maintain a high battery performance.
NiMH battery chargers
Chargers used for charging NiMH batteries are very similar to NiCd battery chargers except that they have more electronics to determine when the battery is fully charged because the drop in voltage at full charge is too small to detect accurately.
They use a combination of sensors to do this, including temperature monitors.
NiMH batteries also require a lower trickle charge (see {{widget type=”cms/widget_page_link” anchor_text=”How does a cordless power tool battery charger work?” title=”How does a cordless power tool battery charger work?” template=”cms/widget/link/link_inline.phtml” page_id=”4031″}}) than NiCd batteries.
NiMH battery chargers that overcharge the battery for a short period improve the capacity of the battery. Unfortunately this is at the cost of charge cycles which can be decreased by 50-100 cycles.
Li-ion battery chargers
Most of the electronics designed to keep a Li-ion battery healthy is in the battery itself but the charger also needs to be able to respond to the battery signals.
Lithium ion batteries have a special protection circuit which ensures the battery never over-charges or over-discharges. Overcharging would cause permanent damage in a lithium ion battery so the charger doesn’t have a trickle charge but stops charging altogether once the battery is full.
Universal battery chargers
Universal battery chargers can charge multiple battery chemistries. They can switch charging style to accommodate whichever battery is being charged. Some can also charge post and slide-on batteries in the same charger.
