It seems one of the problems that face many of us DIY guys is getting NiCad batteries to last longer. Based on what I've read, NiCads last longer with frequent use that includes deep discharge/recharge cycles. That can a problem for the DIY'er who might use a power tool just a few times a year.

The experts say that if you're going to store a NiCad battery, it's best to store it deeply discharged. This seems backward from what most might see as the more logical approach to store them fully charged.

"When storing NiCad batteries, be sure to pick a cool, dry place. The temperature range for storing batteries is between 20 °C and 45 °C. When preparing to store NiCad batteries, be sure to discharge the batteries fairly deeply. The range in recommendations is between 40% and 0% charged when going into storage. NEVER short circuit a NiCad to drain as this causes excessive heat and can cause hydrogen gas to be released…AKA-Boom! The self-discharge rate for NiCad’s is right around 10% at 20 °C, and rising up to 20% at higher temperatures. It is recommended not to store NiCads for an extended amount of time without occasionally using the batteries. Over long periods of storage the cadmium in the NiCad can form dendrites (thin, conductive crystals), which can bridge the gap between contacts and short out the cell. Once this happens, there is really nothing that can be done to fix it long term. The best way to prevent this from happening is frequent use.

One of the most discussed topics about NiCad’s is whether or not they have a ‘memory’. The idea of a charge memory came when they started using NiCad batteries in satellites where they were typically charging for twelve hours out of twenty-four for several years.1 After several years it was noticed that the battery capacity has seemed to have declined severely, and while still operable, they would only discharge to the point that the charger would typically kick in, and then would drop off as if they were completely discharged. For the typical consumer this does not have a large effect, however, we do recommend fully discharging the NiCad you are using before recharging. Occasionally completely draining (but NEVER short circuiting) a NiCad can prevent the on setting of this mysterious battery ‘memory’. An effect with similar symptoms to the memory effect is what is called the voltage depression or lazy battery effect. This is caused by frequent overcharging of the NiCad. You can tell this is happening when the battery appears to be fully charged but discharges quickly after only a brief period use. This is not the memory­ effect, which is limited to NiCad batteries alone, but is something that can happen to any battery, and is almost always from overcharging. Occasionally this can be fixed by running the battery through a few very deep discharge cycles, but doing so can reduce the overall life of the battery. NiCad batteries are the only battery chemistry that benefit from completely discharging before recharging."

https://www.batterystuff.com/kb/articles/battery-articles/what-the-heck-is-a-nicd-battery.html

I just buy Ridgid cordless tools and register them with the company and get free batteries and service for the life of the tool. Now all their batteries are lithium batteries.

When I had no cad batteries, I would occasionally drain to the no go by taping a drill trigger such drill would run slowly. Later, I used a radio to drain.

After this process and recharging a couple of time, batteries were healthy.