About Deep Cycle Batteries
What is a deep-cycle battery?
A deep-cycle battery is built for sustained low-current discharge over many hours, then full or near-full recharge, repeated thousands of times. Internally, deep-cycle batteries use thicker, fewer plates than starting batteries — trading peak cranking current for tolerance of deep discharge. The right choice for off-grid cabin energy storage, RV house bank, marine accessory loads, emergency backup with inverter, and any application where the battery is regularly discharged below 50 % state-of-charge.
UPSPLUSBATTERY.CA stocks deep-cycle batteries in BCI group sizes from Group 24 (~75 Ah) up to 8D (~250 Ah) across flooded, AGM, gel, and LiFePO₄ lithium chemistries. For starting batteries, see marine starting batteries. For chargers, inverters, and inverter-chargers, see chargers and inverters. For solar charge sources, see solar panels.
Deep-cycle chemistries
| Chemistry | Cycle life (50 % DOD) | Usable DOD | Notes |
|---|---|---|---|
| Flooded lead-acid | ~500–1200 cycles | ~50 % | Lowest cost, requires electrolyte maintenance |
| AGM (absorbed glass mat) | ~600–1500 cycles | ~50 % | Sealed, spill-proof, vibration-tolerant, no maintenance |
| Gel | ~500–1000 cycles | ~50 % | Sealed, deep-cycle tolerant, sensitive to overcharge |
| LiFePO₄ lithium | ~3000–7000 cycles | ~80–100 % | Higher upfront, lighter, longer life, BMS required |
For most off-grid cabin / RV / marine deployments, AGM is the workhorse choice — sealed, vibration-tolerant, no electrolyte maintenance. LiFePO₄ is the upgrade tier — higher upfront cost paid back over deployment life through more usable capacity per Ah and more cycles before replacement.
How to choose
Sizing the bank
Determine total daily watt-hour load (sum of each load × hours per day) → multiply by autonomy days (typically 2–3 cloudy days for solar / off-grid) → divide by usable DOD (50 % for AGM, 80 % for lithium) → divide by bank voltage to get total Ah. Example: 1000 Wh/day × 3 days ÷ 0.5 (AGM) ÷ 12 V = 500 Ah at 12 V.
Group size
Match BCI group size to your battery box / mounting hardware. Group 24 (~75 Ah), Group 27 (~95 Ah), Group 31 (~105 Ah), 4D (~200 Ah), 8D (~250 Ah). Physical dimensions and terminal positions vary per group.
Voltage architecture
12 V is the marine / RV / cabin standard. 24 V or 48 V architecture (multiple 12 V batteries in series, or 6 V golf-cart batteries in series) reduces wire size for higher-power inverters above ~1500 W continuous.
Charging
Match the charger to the chemistry. Multi-stage charger with explicit AGM / gel / lithium profile. Lithium needs a CC/CV profile and lithium-compatible BMS. Solar via MPPT controller.
Installation and warranty
Deep-cycle batteries should be installed in a battery box with hold-down hardware to prevent movement. AGM and lithium are spill-proof and accept any orientation; flooded must be installed upright. Wiring sized to the load (refer to current draw at full inverter output). Always install a fuse / breaker at the battery terminal — within 45 cm — sized to 125 % of inverter max current. Manufacturer warranty per brand on individual product pages; UPSPLUSBATTERY 1-year warranty on every battery.
FAQ
Deep-cycle vs starting?
Deep-cycle: sustained low-current discharge over hours, tolerates deep discharge. Starting: brief high-current burst for engine cranking, intolerant of deep discharge. Wrong battery for the job dramatically shortens life — don't use a starting battery as a house bank.
AGM vs flooded?
AGM is sealed, spill-proof, vibration-tolerant, no electrolyte maintenance. Modest cost premium. For most off-grid / RV / marine: AGM is the standard recommendation. Flooded is the budget option in stationary, ventilated, upright-mount applications.
LiFePO₄ worth it?
For long-deployment off-grid (5+ years), high-cycle applications, or where weight matters (RV / marine): yes. ~3× cycle life vs AGM and 80 % usable DOD vs 50 % means a smaller lithium bank can replace a larger AGM bank. Upfront cost is higher; total cost over deployment life is often lower.
50 % DOD — why not deeper?
For AGM and flooded, discharging below 50 % shortens cycle life dramatically — going to 80 % DOD repeatedly cuts cycle life by 60–70 %. LiFePO₄ tolerates 80–100 % DOD without significant life impact, which is why lithium banks can be smaller for the same usable capacity.
Charging time?
AGM bank charges at 10–20 % of bank Ah / hour. 200 Ah bank with a 30 A charger refills 50 % DOD (100 Ah) in roughly 4 hours bulk + 2 hours absorption = ~6 hours total.
Cold weather operation?
AGM and flooded operate down to about –20 °C with reduced capacity. LiFePO₄ should not be charged below 0 °C without a heater (discharge to 0 °C is acceptable). For Canadian winter cabin deployment, ensure the battery box is heated or use heated lithium models.
Disposal?
Lead-acid (flooded, AGM, gel): 99 % recyclable. Municipal hazardous-waste depot, Call2Recycle, retail battery exchange. Lithium: certified lithium-battery recycler — return to us with new pack purchase.
Warranty?
Manufacturer warranty per brand on individual product pages. UPSPLUSBATTERY 1-year warranty on every battery.