Power Tool Batteries. Do’s and Don’ts for Long Life.

How can I get the longest life out of my power tool batteries?

We are going to look at some common practices to help you extend the life of your power tool batteries. But first, we need to understand the battery a little more.

Types of Power Tool Batteries

Take a look inside that power tool battery pack

Whats inside that Battery Pack?

Inside that battery pack is a lot of little rechargeable batteries. Often they are wrapped tightly together with plastic Rechargeable power tool batteries come in mainly three types. Nickle-Cadmium, Nickle-Metal Hybride, and Lithium-Ion. You may be choosing a tool brand and have no idea what type they use.

Nickle-Cadmium = NiCd

Wet-cell nickel-cadmium batteries were invented in 1899. A Ni-Cd battery has a terminal voltage during discharge of around 1.2 volts which decreases little until nearly the end of discharge. Cadmium is considered an environmentally unfriendly chemical and it is being fazed out. So your NiCd batteries are now old school. Even though Cadmium has been banned, since 2006 in the EU, there were exemptions for power tools in the U.S.A until 2016. You can still buy NiCd regular and rechargeable batteries, but they should no longer be supplied in your power tools. Big manufactures are fazing them out compltely by 2022

Good things about Nickle-Cadmium rechargeable batteries are that they can take some abuse, overcharging or over-discharging, without immediate permanent damage. Good pulse power performance makes it a good choice for power tools. They are also cheaper and have a high cycle life and a long overall life of approximately 4 years.

Some bad things about Nickle-Cadmium batteries are the toxic chemicals, the low energy density compared to newer lithium technologies, as well these batteries have the most charge memory and are the heaviest type.

  • Energy density: 50–150 W·h/L
  • Charge/discharge efficiency: 70–90%
  • Specific energy: 40-60 W·h/L
  • Specific power: 150 W/kg
  • Self-discharge rate: 10%/month
  • Cycle durability: 1000-2000 cycles

Nickle-Metal Hybride = NiMH

The Nickle-Metal Hybride battery is a direct replacement for the NiCd cadmium batteries. The chemical reaction at the positive electrode is similar to that of the nickel-cadmium cell, with both using nickel oxide hydroxide. However, the negative electrodes use a hydrogen-absorbing alloy instead of cadmium.

Good things about the Nickle-Metal Hybride batteries are a higher capacity than the NiCd, by 30-40%, higher energy density. And they are less prone to memory. This makes the NiMH battery have longer run times. Another good point is they are a direct replacement for cadmium batteries with little to no change in use parameters. They are more expensive than NiCd but cheaper than Lithium batteries.

Bad things about the NiMH: its relatively low battery life, they can recharge a lot, but will only last typically 2 to 5 years. And they can self-discharge rapidly, with temperature affecting them a lot. Please Note: There is an LSD, low self-discharge, variety and it would be good to check.

  • Energy density: 140–300 W·h/L
  • Charge/discharge efficiency: 66%–92%
  • Specific energy: 60–120 W·h/kg
  • Specifis power: 250–1,000 W/kg
  • Self-discharge rate: 30% but they have a low self dischage type at 0.08–2.9% per month.
  • Cycle durability: 500-1000 cycles

Lithium-ion = Li-ion

The newest type of power tool battery is the Lithium-ion battery. A good thing to note is Lithium, as compared to Lithium-Ion, is not a rechargeable type. Li-ion batteries can deliver up to 3.6 V, three times higher than Ni-Cd or Ni-MH.

Some good things about Lithium Ion rechargeable batteries are they are lightweight for high power, they have very low self-discharge rates, have no memory, and because they have a flexible design, the tools can be well balanced.

The bad things about the Li-Ion batteries are the high cost, short cycle life, and the chance of overcharging which leads to gas.

  • Energy density: 250-693W·h/L
  • Charge/discharge efficiency: 80%-90%
  • Specific energy: 100-265 W·h/kg
  • Specific power: 250–340 W/kg
  • Self-discharge rate: 1.5%-2% per month
  • Cycle durability: 300-500 cycles

Markings on the Battery


Volts are the measurement of tool power. Power tools are mostly 12V, 18V, and 20V Max. Higher voltage means more torque.

Is higher voltage necessary? Yes and No. Yes, you will have more torque for tougher jobs with a higher voltage, but the trade-off is a bigger tool and less run time. With a lower voltage, the amps will go up, so a longer run time and the temperature will stay lower.

Will a 20-volt battery work in an 18-volt tool? Yes! But you will need an adapter that will allow an 18V stem top tool to use the newer 20V MAX batteries. The 20V batteries will not charge on the 18V charger. Because you cannot charge Lithium-Ion batteries in an old charger, you will also need a 20V MAX charger.

New Lithium-Ion battery with an adaptor for NiCd powered tool
New Lithium-Ion battery with an adaptor for NiCd powered tool

Amp Hours

Amp Hours are usually marked on the battery. An Amp Hour refers to the run time on a single charge. It is 1 amp per hour, so 4Ah will deliver one amp for 4 hours, 1.5 Ah, 5Ah, etcetera at the same rate. Amp Hours are also affected by heat, if you run the tool continuously it would heat up and exceed its temp limit. So using a tool sporadically will generally exceed its Amp Hours.

Amp Hours relates to the energy capacity of the battery. In our list, that would be the energy density. The larger the capacity number, the more space available for storage, the longer the run time.

Essentially, the main difference between energy density and power density is that batteries with a higher energy density will be able to store larger amounts of energy, while batteries with a higher power density will be able to release higher amounts of energy a lot quicker. Depending on the type of tool being energized, varying degrees of energy density and power density will be required. Power tools such as jigsaws and circular saws need batteries that can release a lot of energy in one go but at the same time require the battery to have a big gas tank. This means that batteries used to energize power tools need to be high in both energy and power density. 

Best Practice for each type of battery

Always use the charger that came with the tool. Do not mix and match chargers. No type of battery likes getting hot! If your batteries are hot from use, let them cool before charging. Store batteries in a cool dry place, not touching metal or other batteries. Do not store your batteries in the trunk of your car or the garden shed! Inside storage is best.

Nickle Cadmium

Fully discharge before recharge. Cadmium batteries have a memory and it is best to deep-cycle them.

Do not leave them on the charger. Charge for a few days, then store. Re-charge before use if they have sat a long time and self-discharged to nothing. Otherwise, use and recharge when depleted.


Store in a cool, dry place. The battery should be discharged before storage. If the battery is to be stored longer than a year, it should be fully charged and discharged at least once a year to maintain performance

Nickle Metal Hybride

You do not need to fully discharge before recharge. These batteries do not have as big a memory effect.

You can charge a NiMH battery with a NiCd charger. If you are using an older charger, do not leave the batteries on the charger. If you have a newer smart charger, they will cut off when charged to a trickle charge to maintain. NiMH has a high self-discharge rate and can handle a trickle charge.


Try to store at 50%-60% charge level. Due to self-discharge, you’re going to have to check every 2 months to ensure the voltage doesn’t drop below 20%. Humidity should be roughly 40%, a great way to achieve this is to store multiple NiMH batts in a large Tupperware tub.

Lithium Ion

DO NOT fully discharge before recharge. Try not to go below a 20% charge. Shallow discharges and recharges are better than full ones, because they put less stress on the battery, so it lasts longer.

You can charge your lithium-ion battery more often. Once you are at 100% remove the battery from the charger. The chargers do have protection from overcharging once at 100% but if you remove them, they will have a longer overall life.


The Lithium-Ion batteries should be stored at 30%-50% maximum charge for the best results.

How to tell the Power level in my Battery Pack?

With all these different power levels for storage, how do I know what’s left in my power tool battery?

You can use a Multi-Meter to check power levels. You will use the DCV setting on your multimeter, DCV is Direct Current Volts. Set the meter to at least the voltage marked, or just over, so it can read up to the max voltage. The battery pack will have the voltage marked on the side. Touch the probs, negative to negative, positive to positive, and read the voltage.

In a NiCd battery pack, each cell puts out about 1.2V to1.36V and they are joined together to give you the full voltage. There will always be some voltage left even when the battery pack no longer runs your tools. They are considered discharged at 1.1V per cell. Using the tool is the safest way to discharge these types of batteries.

NiMH batteries have a higher capacity, so they hold more power, but they let it out at a similar rate to the Cadmium batteries. They will be fully discharged at 1V per cell.

A lot of newer Lithium-Ion power tool batteries have an indicator on the battery. Just press the button to see the charge level.

Battery indicator on a Lithium-ion power tool battery pack
The battery indicator on a Lithium-ion power tool battery pack

Use your Power Tool Batteries

If you have multiple batteries try to cycle them through the use, charge, store cycle equally. Maybe the best way to do this is to mark them in some way, ie; 1, 2, 3, etc. Use your batteries with confidence, learn what type you have. Treat your batteries according to type. It is best to take the batteries off the charger when done, no matter which type you use.

Remember batteries do not last forever! If you are going to upgrade your batteries, but not your tools, you will need to get more parts. You are going to need new chargers and conversion adaptors. Think about the state of your power tool, and decide if retiring is more cost-effective. Buying tool kits, with new chargers, tools, and new batteries, is something to look into.

When your rechargeable power tool batteries have reached the end of their life do not throw them in the trash. As batteries corrode, their chemicals soak into the soil and contaminate groundwater and surface water. Lithium batteries could even cause a landfill fire. Be responsible and take them to your local hazardous waste pickup.

Leave a Comment

Your email address will not be published. Required fields are marked *