Replacing Rechargeable Batteries in an Cordless Drill

Battery technology has improved since 2007, when I replaced the batteries in a string trimmer. Recently I replaced the batteries in a low cost cordless drill. You can buy a replacement battery pack or replace the cells yourself. The drill I have had a battery pack with ten NiCd 1300 mAh sub-C cells (as fat as a disposable C size battery, but shorter). I found that AA size "pre charged" (or "Low Self Discharge") rechargeable nickel metal hydride (NiMH) cells are now available with 2300 mAh capacity at a reasonable price. So I could replace the batteries with smaller ones with more capacity and which will hold the charge longer.

Nickel-cadmium (NiCd) batteries can be replaced with NiMH, but you may need a different charger. The Lithium batteries used in laptops and newer power tools require very specialized charging and can explode or catch fire if not charged correctly. Only a Lithium battery specifically designed for the tool should be used. Do not substitute lithium batteries for other types.

The first step should be to ensure the battery to be replaced is discharged (check with a multimeter). Then remove the screws holding the pack together. Remove the sub-C cells (ten x 1.2 Volts for a 12 volt pack). Two cell in my pack were holding the battery's connectors in place and I decided to retain these (while electrically insulating them from the new cells with tape).

To make up the new pack I wrapped a strip of silicon self amalgamating tape around one AA cell, then added one next to it and wrapped the tape around both, then a third and fourth. Then I soldered the batteries in series, using a soldering iron and insulated wire. This made a flat pack of four cells held slightly apart by the tape to provide some ventilation and cushioning. I then built another pack of four cells and pushed the two together, held by the stickiness of the tape. I then make a pack of the two remaining batteries and stuck them to the eight, wrapping tape around all. I used some closed cell foam to hold the cells in the battery case. If you are not confident with soldering, you can use a battery holder.

I tested the battery with a multimeter, to make sure the voltage and polarity were correct (and matched that of the charger). Apart from the drill not working correctly, connecting the batteries the wrong way (negative terminal to positive), may damage the drill, the charger or cause the battery to explode.

Longer Life Rechargeable Batteries

Sanyo announced an improved version of their Sanyo Eneloop Low Self-Discharge Rechargeable Battery, 6 October 2009 . These are now avialable in Australia and I purchased two AA cells from Dick Smith Electronics in Canberra.

These are Nickel Metal Hydride (NiMH) rechargeable batteries, which can be charged in the same sort of charger as other NiMH batteries. The main advantage advantage is that the Eneloop batteries will keep a charge for years, while normal NiMH batteries only keep a charge for months. The new batteries are claimed to retain 85% of their charge after a year, whereas normal batteries would be 50% discharged. Also they can be recharged 1,500 times, 500 times more than conventional NiMH batteries.

This makes NiMH batteries practical for low current applications, such as running a clock, where they previously they would not be of use.

Amazon.com adversities the Eneloop in AAA Battery 4 Packs
and the AA batteries in 4 Packs and 8 Packs. There is also mains powered charger with 4 AA batteries and a USB Charger with 2 AA batteries.

There is also a very elaborate "Eneloop Power Pack Kit" 8 AA and 2 AAA Batteries, plus 4 C and 4 D Size adapters.

There is a detailed "Review: Testing Sanyo's Eneloop Low Self-Discharge Rechargeable Battery" avialable, along with a comparison of the new Eneloop against other brand of batteries "Review: Pre-Charged (Low Self-Discharge) Rechargeable Battery Comparison".

It will be interesting to see if the technology is also applicable to batteries for hybrid and electric cars. One of the worrying costs with electric cars is replacing the battery pack. If the battery can be made to last 50% longer, that will reduce the cost. Also a car which can keep the charge longer will be more practical.

Aldi Ready to Use Rechargeable Batteries

Aldi is advertising AA and AAA Ready to Use Rechargeable Batteries. These are in packs of two for AU$7.99. The AA size are 2000 mAh and the AAA 800 mAh. These appear to be low discharge cells, simialr to SANYO eneloop , Sony Cycle Energy and Duracell Pre Charged. The advantage of these batteries is that they hold a useful charge for about a year and are compatible with chargers and devices which use ordinary nickel metal hydride (NiMH) rechargeable batteries.

Pre-charged Nimh C Cell Batteries

The low self discharge AA batteries I installed in a String Trimmer seem to have lost their charge after just under a year. This may be because they were left plugged into a dumb charger (the batteries are supposed to be disconnected from the cgarged when the are charged and then hold their charge). Or perhaps a year is all that can be expected in a heavy duty application from these batteries. Sub C cells, which the trimmer originally had, should offer more power.

Tenergy are offering Pre-charged Nimh C Cells on Amazon.com. The catch is that they are only 3000mAh capacity. It is likely these are actually AA cells fitted into a larger empty metal cylinder to make them up to C cell size. Other C cells are usually 5,000 to 10,000 mHa.

See also:

1. Pre Charged NiMH batteries
2. String Trimmers
3. glue guns
4. Battery chargers
5. replacement battery packs