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1. Rechargeable - Battery Tester
One of the more recent developments in home appliances is the "cordless" feature made possible by nickel-cadmium, sealed-cell, rechargeable batteries and some form of charging device. The charging device is usually a sealed unit which is serviced by direct replacement from the manufacturer, but it rarely is the culprit in battery-operated appliance problems. The most frequent cause of malfunction in these types of appliances is the battery itself. Either it has permanently lost its capacity to take a charge and must be replaced or it has suffered a temporary capacity loss as the result of improper charging procedure. Unfortunately, a low-voltage reading is insufficient to determine whether the loss is temporary or permanent and, as a result, the home-appliance repairman can hardly avoid inadvertently discharging many good batteries. Since the cost of these batteries is considerable it makes good sense to invest in a device which can determine the type of capacity loss, and one that is able to correct the loss should it be temporary. Temporary loss is usually the result of periodic, or "programed" charging sequences which may not be sufficient to counter the state of discharge in the battery. The rechargeable-battery tester corrects this condition by deep-discharging the battery several times and recharging to restore its original capacity. This series of deep-discharges and chargings takes about P/2 hours for the average battery and is fully automatic. If the battery is restored to full capacity, it is an indication of improper operating conditions with regard to the charging unit's ability to restore the battery to maximum capacity. Fitted with several small adapters, this handy unit is capable of testing a wide range of rechargeable batteries from the smallest 1.25V cell to 24V, 2A batteries.
http://www.fun-home-projects.com/electrical_projects/​tools/​rechargeable_battery_tester.html

2. Cordless Appliances
With the development of sealed-cell rechargeable batteries and miniaturized chargers, a large number of appliances have come to be known as "cordless." When these appliances malfunction, the problem is usually low battery voltage. See Chapter 2 for a discussion of chargers and charging techniques. We will use Disston's grass shears as a representative example of this class of appliances. Troubleshooting The shear runs below normal speed. Check the charger output with a VOM. The reading should be between 2.3 and 3.6V. If not, replace the charger since repairs are impractical. Next, check the battery pack by putting it on charge overnight. If the shear still does not develop normal speed and power, replace the battery pack. Remove the terminal assembly from the shear and inspect for bad or intermittent connections. There should be a potential of 10V between the positive and negative terminals. Wiggle the terminals as you make the reading. No voltage means that the wiring is broken and needs replacement. The shear operates for only a short period (less than 45 minutes) between charges. The first thing to look for is binding in the mechanism which would cause the motor to draw more current. Remove the blades and check for any deflection or obstruction in the gear teeth. Check to make certain the blades are not set too close together. The upper blade teeth should barely contact the lower blade teeth. With the blade mechanism installed, the motor should draw between 1.4 and 2A. Replace the blade assembly if the mesh is off, the blades are dull, or the meter reading fails to stay within specifications. Next, check the motor for faulty operation. Remove the motor from the shear. Check with a known-good battery pack. The current reading ought to fall between 0.9 and 1.2A. Should the reading be higher, replace the motor. Noisy operation may be traced to wear on the gear train, cam, or ring insert. If the gears are still good and the blades sharp, replace the ring. The armature side-to-side play should be no more than 1 / 32" and preferably less. Individual spares are not available; replace the motor as a unit. If the blades jmain motionless while the motor runs, check for stripped gear teeth and for a loose drive pinion. A loose pinion means that the motor and pinion must be replaced. No blade movement and no motor sound usually means a failure in the electrical circuit. Check the battery pack, wiring harness, switch, and motor. The switch contacts should arc slighdy as they are opened. Disassembly Disassembly is not difficult. Take out the three housing screws from the right side of the housing. Separate the parts. Next, remove the lock-button assembly by lifting the lock button out of its slot in the switch plate. This frees the switch button from its slot in the switch-button plate. Remove the contact switch from the shear by disconnecting the positive (red) battery wire from the top leaf of the switch and the positive motor wire from the bottom leaf. Now remove the terminal-board assembly by disconnecting the battery and motor leads. Take out four blade screws from the blade-base housing and remove the blade assembly from the base. To separate the blades, turn the top one 90 degrees to the bottom one and push the blade insert out from between them. Remove the large cam gear and the small combination gear from the blade-base housing . Then remove the motor-mounting screws and free the motor.
http://www.fun-home-projects.com/electrical_projects/​repairs/​cordless_appliances.html

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