Deep cycle batteries

A deep cycle battery is built to deliver steady power for hours and to be recharged over and over, not to crank an engine. Pick yours by the numbers: Ah capacity, discharge rate, cycle life, chemistry and case size.

Narrow the list by 6, 8 or 12 V and by AGM, GEL, flooded lead-acid or LiFePO4 to find the model that suits your equipment.

How it differs from a starter battery

A starter battery packs many thin plates to release hundreds of amps for a few seconds. A cyclic battery uses thicker plates and denser active material, designed for slow, deep discharges. Put a car battery in a wheelchair or a camper and it will lose capacity within weeks.

Reading the datasheet

• Capacity and rate: always compare at the same rate. A C20 figure (20-hour discharge) reads higher than a C5 one; for traction and mobility, C5 is closer to real use.
• Cycles and depth of discharge: cycle life is quoted at a given DoD (50 %, 80 %). The less you drain the battery, the more cycles you get.
• Chemistry: AGM is maintenance-free and handles high currents; GEL tolerates deep discharge and heat better; flooded gives plenty of cycles but needs topping up; LiFePO4 is light and lasts thousands of cycles with the right charge profile.
• Size and terminals: check length, width, height and terminal type (M6/M8 thread, faston, taper post).

Choose by application

Electric wheelchairs and mobility scooters usually run on 12 V blocks up to about 90 Ah. The leisure circuit of motorhomes and caravans calls for 12 V above 120 Ah. In an off-grid solar system, daily energy use and days of autonomy set the size.

FAQ

Can I use any charger on a deep cycle battery?

Better not. Each chemistry needs its own absorption and float voltage. Use a charger with an AGM, GEL or lithium curve to match the battery.

Can I mix new and used batteries in a series bank?

Avoid it. The weakest unit limits the whole string and ends up over-discharged. Replace the full set with the same model.

How should I store it over winter?

Fully charged, in a cool and dry place. Lead-acid batteries slowly self-discharge, so top them up every few weeks or leave them on a maintenance charger.