STIHL AP battery on charge

It’s not uncommon to hear about the memory effect in some batteries, causing them to lose their energy capacity with repeated partial charging. Once the battery’s power drops, the operating time of your cordless power tool is reduced, leading to the battery needing to be charged more frequently. Thankfully not all batteries are affected by this loss of capacity, and memory effect is not an issue for STIHL lithium-ion batteries. They can be charged at any time, regardless of their existing charge level.

Battery Memory Effect: Discovered in the 1960s

STIHL AP 300 S Battery plugged into a STIHL cordless toolBattery memory effect was discovered by engineers in the 1960s who noticed that batteries used in a satellite lost their capacity over time. They found that under certain conditions where the battery was repeatedly partially discharged to 25% then fully recharged, the batteries would only supply the amount of energy added with the most recent charging process; the previously charged residual power was not available for use.

To explain further, imagine a suitcase. Instead of unpacking the last items, you fit a permanent false bottom. The new space is now all the storage your suitcase can offer; there is less space to fill and you can’t access what you’d previously packed. In batteries, the memory effect manifests as a voltage drop, and can eventually cause affected batteries to become unusable when the voltage falls below the minimum requirement of the power tool.

Battery memory effect isn’t the only culprit for voltage drops however. Over charging, deep discharge and over-heating can also result in a reduction of the charged voltage and affect the performance of the battery. Thankfully, all STIHL lithium-ion batteries include preventative measures against all these risks:

  • All STIHL chargers turn off automatically when the battery is fully charged to prevent over-charging. STIHL AL 300 and AL 500 batteries also feature a fan to cool the batteries as they charge.
  • All batteries have residual charge left even when the charge level indicator is indicating otherwise. This protects against deep discharge in the short term, but if you are storing the batteries for longer periods, we do recommend storing them between 40-60% charged.
  • If the internal temperature of the battery reaches a set point, the battery automatically deactivates until it is suitably cooled.

STIHL AP Battery ready to be used in a cordless chainsawWhich Batteries are Susceptible to Memory Effect?

Battery memory effect mainly occurs in nickel-cadmium batteries (NiCd), which used to be widely used in cordless tools. In these batteries the effect is caused by the formation of crystals on the cadmium cathode, because if the battery isn’t fully discharged the crystals can form in the undischarged portion of the battery cell. The voltage decreases as the crystals grow in size, due to the crystals impairing the conductivity of the material. Nowadays, these types of batteries are rare.

Quality STIHL Lithium-ion Batteries

STIHL Battery plugged into the STIHL AL 301 chargerSTIHL only uses advanced lithium-ion batteries which are not only lighter and more powerful than their predecessors, but are almost completely unaffected by the memory effect. They show no appreciable voltage decrease after repeated partial discharge thanks to the materials and cutting-edge technology we use in our battery cells. STIHL lithium-ion batteries can be charged at any time and it doesn’t matter if you don’t always charge the battery to full before using it. There’s no need for any clever charging tips, as even a brief charge between jobs poses no risk. For more information on STIHL batteries, check out our top 10 ways to get the most from your battery blog post.