Most returns to the factory turn out to be for problems other than a defective charger. A few simple tests can help to track down the cause of poorly operating charger-battery system.
When a charger fails, it usually puts out a very low voltage and virtually no current. Or it puts out a large voltage (around 22V for a 12V charger, or 35V for a 24V charger) and a current above the published range (if a battery is connected).
Measure the output current limit (using a discharged battery as a load) and the output voltage (using a charged battery). If the outputs are not within spec, then the charger is defective and should be returned for repair. If the outputs are within spec, the charger is OK and the problem is elsewhere (usually a damaged battery).
There are a few other scenarios that might seem to be a charger problem but, actually are a problem with the application circuit.
Low Output Voltage/Normal Output Current: There is a severe load on the charger - possibly by an over-discharged battery, a battery with a shorted cell, or an excessive current drain in the application circuit.
Isolate the excessive load by measuring the current going into the battery and into the application circuit. A battery that continues to draw a large current without becoming recharged, probably has a shorted cell and should be replaced.
Consider swapping with a new battery as a quick test.
Charger "Locks" in Bulk Mode: Again, a battery with a shorted cell is the most likely culprit. The charger will try (in vain) to recharge the battery and the battery will, quite often, become warm as the full charger current continues to flow through the remaining good cells.
Measure the current flowing into the battery. A healthy battery will draw a diminishing current as it becomes recharged - even if the charger is in bulk or absorption mode (elevated voltage). A battery with a shorted cell will continue to draw a large current from the charger.
Charger "Locks" in Absorption Mode after Charging LED Goes Out:
Power Transformer Gets Hot: The power transformers used in all chargers are UL/CSA recognized and have insulation rated for 150C. The transformer's temperature should never get to 150C under normal operating conditions - even at the charger's maximum rated ambient temperature. However, the transformer will normally run at around 65C to 75C at a room temperature ambient (when under full load). This will feel quite hot to the touch but is safe and normal.
The Chassis Gets Hot: Many of the chargers use the aluminum chassis as a heatsink for the charger's series-pass power transistor. The area of the chassis is sufficient to allow safe operation even if the chassis is not bolted to a metal frame (which draws some of the heat from the chassis) as long as the ambient temperature is within published specs.Trying to operate the charger in a too-small and/or poorly ventilated enclosure may cause the ambient to rise above maximum limits and should not be allowed. Mounting the charger on a DIN rail eliminates possible
The On-Board Heatsinks Get Hot: The small clip-on heatsinks used on-board with some chargers can normally get hot - too hot to touch comfortably.
Power semiconductors can run safely at surprisingly high temperatures.
While the reliability and life of a semiconductor certainly is reduced as the temperature rises, it is the electrolytic filter capacitors that ultimately determine the life and reliability of most chargers or power supplies.
For this reason, all Ibex