Best replacement batteries for battery backup sump pumps

Start here: Basement Watchdog Deep Cycle AGM Battery (B2200). It's the sealed AGM deep-cycle pack built for backup sump systems — no topping up with water, safe to sit on a basement floor, and it's the cheapest of the true deep-cycle AGM options here. If your pump is a Basement Watchdog unit, this is the direct fit.

Who the others suit:

• Wayne Deep Cycle AGM (75 Ah) — if you run a Wayne backup pump, or want a bigger reserve for long outages.
• VMAX XTR34-75 / SLR125 — the step up for big basements or high-water-table pits; the 125 Ah version gives the longest runtime.
• Basement Watchdog AGM standby — same family, slightly larger case; check your pump's tray dimensions before ordering.
• Optima BlueTop — rugged and vibration-tolerant, but overkill unless you also want it for a boat or RV.
• EverStart marine deep cycles — budget-friendly and widely available, but flooded lead-acid: they need ventilation and water checks.
• MightyMax 3 Ah — a small alarm/electronics battery, not a pump battery. Skip it.

Whatever you pick, match the voltage and terminal type to your pump's charger, and keep the battery on a trickle charger so it's full when the power drops.