Deep-cycle batteries are made for repeated discharge and recharge, but a symptom such as short runtime or incomplete charging does not identify a single fault. First record the battery’s make, model, chemistry, age, connected loads, charger model, and the conditions when the problem appears. Use the battery and charger manuals for the exact tests and limits.
What are deep-cycle batteries used for?
Deep-cycle designs are intended for repeated energy use. Trojan lists applications including golf cars, marine, RV, and solar systems. A deep-cycle label alone does not identify chemistry, capacity, allowable discharge, charging profile, or compatibility with a particular system. Confirm those details in the model’s documentation.
Runtime is shorter than expected
Compare the current load and operating conditions with the battery’s rated capacity and test conditions. Trojan’s maintenance guidance explains that voltage and specific-gravity readings, when applicable to the battery, can help assess charge, age, and health; they may also indicate a weak battery. Use the manufacturer’s procedure and interpret results against that model’s specifications. A charger’s “full” light by itself does not measure usable capacity.
The battery does not appear to charge fully
Check that the charger is designed for the battery chemistry and follow both manufacturers’ charging instructions. Record the charger’s indicators and the time taken, then use the battery maker’s approved checks or ask a qualified technician to test it. Avoid generic voltage cutoffs: charge readings vary with chemistry, temperature, rest time, and the manufacturer’s test method.
Charge falls during storage
Trojan notes that batteries self-discharge during storage and that storage conditions and maintenance affect charge. Disconnect or account for any connected equipment, follow the model’s storage and recharge schedule, and investigate unexplained loss using the maker’s test procedure. Do not assume every idle battery has a defect.
Keep care specific to the battery
Watering and equalization instructions apply only when the battery maker specifies them for that design, such as certain flooded lead-acid batteries. Do not apply flooded-battery procedures to AGM, gel, or lithium packs. Follow the manual for ventilation, charging, and service; stop and seek qualified help if the battery is damaged or behaves abnormally.
Related: See whether a regular charger can charge a deep-cycle battery, compare a deep-cycle battery amp-hours chart, and browse our Group 31 deep-cycle battery guide.
Sources: Trojan Battery: Selecting Deep Cycle Flooded Batteries; Trojan Battery: Battery Maintenance
