Overworking the battery can have a detrimental effect on its performance and life. For example, if the truck is worked well beyond the normal rating of its battery ... for example, by repeatedly lifting very large loads very fast for a long time ... it is possible for the battery voltage to fall below the manufacturer's specified end point. While it is true that letting the battery recover (for a time that may extend from minutes to hours, depending on the depth of discharge) will bring it back to a useful state-of-charge, it is also true that repeated heavy discharges of this kind can damage the plates by overheating, sulfation and cell (polarity) reversal.
The makers of trucks and their electrical components offer another set of objections to overworking the battery. Operating at lower-than-specified voltage can do irreparable damage to relays, SCRs (Silicon Controlled Rectifier), contactors, motors, etc.
Damage to a battery and/or a truck caused by deep discharge is the result of failure to detect the 80% discharge point of the battery and its continued use. In the case of component failure, inadequate maintenance is often at fault.
The use of a reliable, accurate and repeatable "fuel" gage on the truck will always prevent both battery and truck damage because the "fuel" gage will always detect the 80% recommended discharge limit. A properly designed "fuel" gage with a lift lockout will actually prevent the driver from working the truck past this limit and will force him to return for battery charging.
To get the most out of traction batteries, every truck should be equipped with a reliable, accurate, repeatable "fuel" gage and controller; operating procedures should be arranged so that batteries are placed on charge only when 80% discharged; chargers should be maintained in good operating condition; and a regular routine of inspection and preventive maintenance should be followed. To do less is to waste energy, time, and money.