A deep cycle battery is a lead acid battery built to be discharged and recharged over and over, unlike a car battery, which is made to give a short burst to start an engine. The usual size for backup is a 12 V battery of 100 to 105 Ah, in flooded, AGM or gel form. They cost less upfront than lithium, but they are heavy and should not routinely be run below about half their capacity. This page covers the types, depth of discharge, charging and when they still make sense. Send one request for free, no-obligation quotes.
Flooded, AGM and gel
- Flooded (wet) batteries are the cheapest. They give off gas when charging, so they need a ventilated space, and the water level must be checked and topped up with distilled water.
- AGM batteries are sealed, need no topping up and handle higher currents well. They suit inverters and trolleys indoors.
- Gel batteries are sealed and cope with deep, slow discharges and heat a little better, but need a charger with a gel setting.
Whatever the type, check it is sold as deep cycle or solar, not a starter battery with a new sticker.
Depth of discharge: the 50% rule
Lead acid lasts longest when it is not run flat. As a rule of thumb, use about half of the rated capacity and recharge. A 12 V 100 Ah battery holds about 1.2 kWh on paper, so plan on roughly 0.6 kWh of useful energy. Run it to empty night after night and its life shortens quickly. This is why a lead acid bank must be about twice the size of a lithium one for the same backup. Leaving a battery partly discharged for days also harms it.
Charging and ventilation
Lead acid needs a full charge after each use, which takes hours, and a long recharge can be a problem when outages come close together. The inverter or charger must be set to the right type (flooded, AGM or gel). Keep batteries in a cool, ventilated place off direct sun: heat shortens their life and flooded batteries release hydrogen when charging. In a bank, every battery should be the same type, size and age, joined with equal length cables.
When deep cycle is still the right choice
Lead acid still makes sense for a tight budget, a small trolley used now and then, a system that seldom cycles, very cold sites where lithium may not charge, or as a like-for-like swap in an older inverter that has no lithium setting. For daily use behind a home inverter, lithium batteries usually cost less over their life. Old lead acid batteries are worth money to scrap dealers: see battery recycling.
What to include in your request
- How many batteries and the size you need
- Flooded, AGM or gel, or ask for advice
- Your inverter or charger and its settings
- Where the batteries stand and the ventilation
- Whether the old batteries go back
Deep Cycle Batteries for different clients
- Homeowners: deep cycle batteries in a trolley or small inverter for lights and wifi
- Complexes, estates and body corporates: AGM batteries backing up guard huts, intercoms and boom gates in outages
- Offices and home offices: a small deep cycle bank behind an inverter for a few desks and the router
- Shops, restaurants and salons: AGM batteries keeping a till, card machine and lights going during outages
- Farms and smallholdings: flooded deep cycle banks in a ventilated shed for the fence and lights
- Clinics, surgeries and care homes: sealed deep cycle batteries for small inverters at rural clinics
- Factories, warehouses, schools and churches: deep cycle banks for workshop lighting, alarms and older inverters
- Electricians, installers and security companies: auto electricians and installers buying 100 Ah deep cycle batteries in bulk
Frequently asked questions
How much is a 100Ah deep cycle battery?
Can I use a car battery instead of a deep cycle battery?
AGM or gel deep cycle battery: which is better?
How do I get quotes for deep cycle batteries?
Deep Cycle Batteries by province and city
- Johannesburg
- Pretoria
- Centurion
- Midrand
- Sandton
- Randburg
- Roodepoort
- Krugersdorp
- Randfontein
- Germiston
- Boksburg
- Benoni
- Kempton Park
- Alberton
- Vanderbijlpark
- Vereeniging
- Durban
- Pinetown
- Pietermaritzburg
- Richards Bay
- Newcastle
- Ladysmith
- Gqeberha (Port Elizabeth)
- East London
- Kariega (Uitenhage)
- Mthatha
- Cape Town
- Bellville
- Paarl
- Stellenbosch
- George
- Worcester
- eMalahleni (Witbank)
- Middelburg
- Secunda
- Mbombela (Nelspruit)
- Rustenburg
- Brits
- Klerksdorp
- Potchefstroom
- Mahikeng
- Polokwane
- Tzaneen
- Kimberley
- Upington
- Bloemfontein
- Welkom
- Sasolburg