Battery drains fast on heavy equipment: alternator or parasitic drain?

A battery that drains quickly is a frustrating problem, especially when the machine is on a remote site. The cause is usually one of three things: the battery has reached the end of its life, the alternator isn't charging properly, or something is drawing power while the machine is off.

Heat shortens battery life

In the Saudi summer, batteries last much less than average. A two- or three-year-old battery that drains quickly has usually reached the end of its life, even if it worked well before.

Test with a multimeter

1. With the engine off after the machine has rested for hours: a healthy charged battery reads about 12.6 V (or 25.2 V on a 24 V system).
2. Start the engine and measure at the battery terminals: it should read about 13.8 to 14.4 V (or 27.6 to 28.8 V on a 24 V system). If it reads the same as with the engine off, the alternator isn't charging.
3. A reading above 15 V (or 30 V on a 24 V system) means the alternator is overcharging, which damages the battery.
4. Check the alternator belt: is it loose or slipping?

Other causes

• Corroded or loose battery terminals preventing a full charge.
• A damaged or corroded ground strap between the engine and the frame.
• Lights, a radio or a tracking device drawing power with the machine off.
• A stuck relay keeping part of the electrics switched on.

Summary

Start with the terminals and belt, then test charging with a meter. If the alternator is fine and the battery is old, replace the battery. If the alternator isn't charging, replace or repair it before it ruins a new battery.