Best Sump Pump Backup Battery

Battery powered sump pumps are type of emergency equipment that must operate reliably when required, and saving the money on these pumps or their batteries may be very expensive thing to do.

Sump pump backup battery must be strong enough to power sump pump motor and it must store enough energy to power the whole unit long enough to prevent as much damage as possible until mains power is restored.

wayne esp25 sump pump

Battery Powered Sump Pumps Features and Specifications

The most important feature of the battery powered sump pump is the nominal strength of the pump motor and it is usually given in the HPs. Commonly battery operated sump pumps come with 1/6 HP, 1/4 HP, 1/3 HP, 1/2 HP, 3/4 HP or even 1 HP motors.

Note: Mains powered sump pumps, especially those powered by three phase electric power may feature several HPs motors, but these are mostly commercial units, rarely used at homes.

Most common type of battery operated sump pumps are 12V sump pumps, with 24V sump pumps being used where larger flow (gallons per hour) or larger lift (given in feet) is required:

- 12V sump pumps, normal conditions: go for single, high-quality AGM battery,

- 12V sump pumps, long operating time required: go for 2 or more, high-quality AGM batteries and connect them in parallel - use the same battery model of the same brand, preferably from the same batch,

- 24V sump pumps: choose 2 high-quality AGM batteries and connect them in series.

Most popular sump pumps come with their own battery boxes and their own battery chargers, somewhat limiting the users regarding battery selection.

But, in the case of emergencies, one has to know that sump pumps don't operate continuously. For example, some motor controllers when alarm is triggered, will run pump motor for 10-20 seconds continuously (to prevent short cycling), but after that next alarm my be hours away.

In the case of 'worst case scenario' emergency, one may assume that the basement will be fully flooded and that sump pump will work continuously until the battery is fully discharged - and that is really worst case scenario! In that case, it is important to know how many gallons sump pump may pump out on the single battery charge, depending on the required height.

All these values are good to know BEFORE choosing and installing battery powered sump pump.

Sump Pump Battery Boxes and Chargers

Sump Pump battery chargers operate as both chargers and maintainers, keeping the battery fully charged and in optimal condition over long period of time.

If the sump pump doesn't have a reliable battery charger/maintainer, consider buying dedicated one and connect it to the battery.

Note: battery powered sump pump and similar emergency equipment MUST work reliably in the case of emergencies - if they don't operate reliably, what's the point of having them? Thus, any work on sump pump and their electric and electronic systems should be done by certified personnel, or at least by someone who actually knows what to do. Seriously!

odyssey 31m pc2150st m battery 2Preferred battery type of sump pump batteries are AGM (Absorbent Glass Mat) SLA (Sealed Lead Acid) batteries which are practically maintenance free and often may operated in any position. Flooded/wet cells batteries are not maintenance free and may fail when absolutely needed.

Lithium ion batteries are also possible choice for sump pump batteries, but although they are lighter and often may withstand large number of charging/discharging cycles, sump pump batteries most of their operating lifetime spend in waiting - standby type of application.

Car batteries are designed as starting/cranking batteries, being able to provide short burst of power for shorter period of time and thus are not best choice for, what is easily possible, deep cycle applications. However, if your sump pump battery is dead for who knows what reason, hook your charged car battery and let it work - one(!) deep discharge cycle will not harm starting battery, but the cycle use may shorten it operating life significantly.

Thus, when choosing sump pump battery, go for reliable deep cycle (or maybe dual purpose) AGM battery from the reputable brand.

Most sump pump battery boxes accept BCI Group 27 batteries or BCI Group 31 batteries.

Their sizes are:

- Group 27 batteries (L x W x H): 12.0625 x 6.8125 x 8.875 (12 1/16 x 6 13/16 x 8 7/8) inches, 30.6 x 17.3 x 22.5 cm,

- Group 31 batteries (L x W x H): 13 x 6.8125 x 9.4375 (13 x 6 13/16 x 9 7/16) inches, 33 x 17.3 x 24 cm.

As one can see, battery box designed to accept group 31 battery may also accept group 27 battery or any other battery group that is smaller than group 31 battery. However, smaller the battery, smaller the capacity in Ah and thus, shorter the operating time of the sump pump when there is no mains power available.

Following two charts list the most popular group 27 and group 31 dual purpose and deep cycle batteries.

Most Popular Group 27 Batteries

Model Battery Type Chemistry Ah MCA RC Weight Review
GreenLiFE GL80-80AH Deep Cycle LiFePO4 80 - - 28 lbs; 12.8 kg -
Mighty Max ML100-12 Deep Cycle AGM 100 - - 63.9 lbs; 29 kg -
NorthStar NSB-AGM27 Dual Purpose AGM 92 1080 195 68 lbs; 31 kg NSB-AGM27, 27F, 27M
Optima 8027-127 D27M Dual Purpose AGM 66 1000 140 54 lbs; 24.5 kg D27M & D27F
UPG UB121000 Deep Cycle AGM 100 - 170 64 lbs; 29 kg -
VMAXTANKS MR127-100 Deep Cycle AGM 100 800 200 68 lbs; 31 kg MR127-100
VMAXTANKS SLR100 Deep Cycle AGM 100 - 220 68 lbs; 31 kg -
VMAXTANKS XTR27-110  Deep Cycle AGM 110 880 220 68 lbs; 31 kg -

Note: Amazon links in the table open in the new windows ('Model' column), so feel free to check them for most up-to-date prices and offers.

On average, Group 27 AGM batteries feature 20h capacity in the 90-100 Ah range, with Reserve Capacity (RC) values of 190-220 minutes.

Note: Optima batteries use spiral wound cells and are somewhat lighter than other batteries of similar size and feature smaller capacity and shorter RC. Other than that, they are popular and rather reliable batteries.

Most Popular Group 31 Batteries

Model Battery Type Cell Type Ah CCA MCA RC Weight (lbs/kg) Review
Battle Born 100Ah 12V LiFePO4 Deep Cycle LiFePO4 100 - - - 29 lbs; 13.2 kg Battle Born 100 Ah 12 V LiFePO4 
Exide XMC-31 Deep Cycle AGM 100 925 1110 200 68 lbs; 31 kg -
GreenLiFE Battery GL100 Dual Purpose LiFePO4 100 - 1000 - 28 lbs; 12.7 kg -
Lifeline GPL-31T Deep Cycle AGM 105 600 750 195 69 lbs;  31.5 kg -
Lifeline GPL-31XT Deep Cycle AGM 125 650 800 230 69 lbs; 31.5 kg -
Lifeline GPL-3100T Dual Purpose AGM 100 810 950 228 67 lbs; 30.4 kg -
NorthStar ELT-AGM31 Dual Purpose AGM 100 925 1050 190 65.7 lbs; 29.8 kg -
NorthStar NSB-AGM31 Dual Purpose AGM 103 1150 1370 220 75 lbs; 34.0 kg -
NorthStar NSB-AGM31M Dual Purpose AGM 103 1150 1370 220 75 lbs; 34.0 kg  -
Odyssey 31M-PC2150 Dual Purpose AGM 100 1150 1370 205 77.8 lbs; 35.3 kg  Odyssey 31M-PC2150 
Optima 8052-161 D31M Dual Purpose AGM 75 900 1125 155 59.8 lbs; 27.1 kg Optima D31M BlueTop 
Trojan T31 Deep Cycle Gel 102 - - 200 70 lbs; 31.7 kg -
VMAXTANKS SLR125 Deep Cycle AGM 125 - - 260 75 lbs; 34 kg -
VMAXTANKS MR137-120 Deep Cycle AGM 120 - 900 230 75 lbs; 34 kg -
XS Power XP3000 Deep Cycle AGM 120 - - 240 73 lbs;  33.1 kg -
WindyNation BAT-NSAP12-100 Deep Cycle AGM 106 - - - 67 lbs; 30.4 kg -
 

Note: Amazon links in the table open in the new windows ('Model' column), so feel free to check them for most up-to-date prices and offers.

On average, Group 31 AGM batteries feature 20h capacity in the 100-125 Ah range, with Reserve Capacity (RC) values of 200-260 minutes.

For smaller sump pump motors (1/2 HP or less), it is recommended to go for deep cycle/solar batteries, while for stronger sump pump motors (3/4 HP or more), it is recommended to choose dual purpose batteries.

Reason is simple - at 1/2 HP (US HP -> 746W), 12V motor draws at least 31.1 Amps, and that is not a problem for 100Ah deep cycle AGM batteries. However, at 3/4 HP, 12V motor draws at least 46.7 Amps and dual purpose batteries generally perform better. At 1 HP, 12 motor draws at least 62 Amps and actual capacity of deep cycle batteries optimized for low discharge applications may deteriorate too much.

Rule of thumb: don't overthink - go for reputable brand, just check the size of the battery and its Reserve Capacity value.

Sump Pump Motors Operating Time Charts

One of the most popular and affordable 100 Ah batteries is Mighty Max ML100-12 100 Ah AGM deep cycle battery.

Following charts list Mighty Max ML100-12 discharging features - constant current discharge characteristics (in Amps, at 77°F/25°C) and constant power discharge characteristics (in watts, also at 77°F/25°C):

End Voltage Per Cell Battery End Voltage 10 min 15 min 30 min 45 min 1 hour 3 hours 5 hours 10 hours
1.60 V 9.6 V 207 162 92.0 66.5 53.5 24.0 16.2 9.20
1.65 V 9.9 V 195 154 89.3 65.1 52.5 23.5 16.0 9.15
1.70 V 10.2 V 183 145 86.4 63.6 51.3 23.0 15.7 9.10
1.75 V 10.5 V 170 136 83.2 62.0 50.0 22.5 15.4 9.05
1.80 V 10.8 V 155 126 80.0 60.0 48.5 21.8 15.0 9.00
End Voltage Per Cell Battery End Voltage 10 min 15 min 30 min 45 min 1 hour 2 hours 3 hours 5 hours
1.60 V 9.6 V 2250 1830 1032 750 618 372.0 280.8 189.0
1.65 V 9.9 V 2178 1734 1008 738 606 366.0 276.0 187.2
1.70 V 10.2 V 2100 1686 978 726 594 358.2 270.6 185.4
1.75 V 10.5 V 2010 1626 948 708 582 349.2 265.2 183.0
1.80 V 10.8 V 1890 1548 912 690 570 339.6 259.6 180.0

Note: listed values are average values and they vary slightly from the battery to the battery.

mighty max ml100 12Sump pump motors come in different sizes:

- 1/6 HP: ~125 W, ~10.5 Amps, 5+ hours.

- 1/4 HP: ~187 W, ~15.6 Amps, ~5 hours, but end-voltage is rather low.

- 1/3 HP: ~250 W, ~21 Amps, 3+ hours,

- 1/2 HP: ~375 W, ~31.5 Amps, almost 2 hours,

- 3/4 HP: ~560 W, ~46.7 Amps, 1+ hour,

- 1 HP: ~746 W, 62.2 Amps. around 45 minutes, but end-voltage is rather low.

These values are given for the brand new, fully charged battery. Also note that sump pump motors are not working constantly, and these values are for constant operation.

For example, sump pump feature 12V 1/2 HP motor and it operates 15 seconds every 30 minutes. In that case, one may expect this battery to power such sump pump for ~10 days! If there are issues with the underground water levels and such motor operates 15 seconds every 1 minute, one may expect this battery to power such sump pump for ~8 hours.

Mighty Max ML100-12 offers good performances at acceptable price, however, if the money is not of an issue, there are better performers, for example:

- Group 27 batteries: VMAXTANKS XTR27-110 (220 min RC), or

- Group 31 batteries: VMAXTANKS SLR125 (260 min RC).

Note: Author of this article is biased toward Odyssey batteries and he can recommend Odyssey 31M-PC2150 for almost any situation, especially during cold weather - obviously, its starting features are definitely an overkill for sump pump battery, but ...

Also, it is not a cheap battery, but it can withstand so much use and abuse - industrial workhorse battery :)


Long Story Short: Best sump pump battery must be reliable and must tolerate float/standby use well - for at least 5-7 years, preferably 8+ years.

AGM SLA batteries are practically maintenance free batteries, offering great reliability at affordable price.

When looking for new sump pump battery, check dimensions of available battery box/battery compartment and go for reliable deep cycle/dual purpose battery from reputable brands - don't go cheap since your home may depend one day on this battery.

Most common sump pump batteries are group 27 and group 31 batteries, so choose according to your own needs and preferences:

Model Battery Type Chemistry Ah MCA RC Weight Review
GreenLiFE GL80-80AH Deep Cycle LiFePO4 80 - - 28 lbs; 12.8 kg -
Mighty Max ML100-12 Deep Cycle AGM 100 - - 63.9 lbs; 29 kg -
NorthStar NSB-AGM27 Dual Purpose AGM 92 1080 195 68 lbs; 31 kg NSB-AGM27, 27F, 27M
Optima 8027-127 D27M Dual Purpose AGM 66 1000 140 54 lbs; 24.5 kg D27M & D27F
UPG UB121000 Deep Cycle AGM 100 - 170 64 lbs; 29 kg -
VMAXTANKS MR127-100 Deep Cycle AGM 100 800 200 68 lbs; 31 kg MR127-100
VMAXTANKS SLR100 Deep Cycle AGM 100 - 220 68 lbs; 31 kg -
VMAXTANKS XTR27-110  Deep Cycle AGM 110 880 220 68 lbs; 31 kg -

Model Battery Type Cell Type Ah CCA MCA RC Weight (lbs/kg) Review
Battle Born 100Ah 12V LiFePO4 Deep Cycle LiFePO4 100 - - - 29 lbs; 13.2 kg Battle Born 100 Ah 12 V LiFePO4 
Exide XMC-31 Deep Cycle AGM 100 925 1110 200 68 lbs; 31 kg -
GreenLiFE Battery GL100 Dual Purpose LiFePO4 100 - 1000 - 28 lbs; 12.7 kg -
Lifeline GPL-31T Deep Cycle AGM 105 600 750 195 69 lbs;  31.5 kg -
Lifeline GPL-31XT Deep Cycle AGM 125 650 800 230 69 lbs; 31.5 kg -
Lifeline GPL-3100T Dual Purpose AGM 100 810 950 228 67 lbs; 30.4 kg -
NorthStar ELT-AGM31 Dual Purpose AGM 100 925 1050 190 65.7 lbs; 29.8 kg -
NorthStar NSB-AGM31 Dual Purpose AGM 103 1150 1370 220 75 lbs; 34.0 kg -
NorthStar NSB-AGM31M Dual Purpose AGM 103 1150 1370 220 75 lbs; 34.0 kg  -
Odyssey 31M-PC2150 Dual Purpose AGM 100 1150 1370 205 77.8 lbs; 35.3 kg  Odyssey 31M-PC2150 
Optima 8052-161 D31M Dual Purpose AGM 75 900 1125 155 59.8 lbs; 27.1 kg Optima D31M BlueTop 
Trojan T31 Deep Cycle Gel 102 - - 200 70 lbs; 31.7 kg -
VMAXTANKS SLR125 Deep Cycle AGM 125 - - 260 75 lbs; 34 kg -
VMAXTANKS MR137-120 Deep Cycle AGM 120 - 900 230 75 lbs; 34 kg -
XS Power XP3000 Deep Cycle AGM 120 - - 240 73 lbs;  33.1 kg -
WindyNation BAT-NSAP12-100 Deep Cycle AGM 106 - - - 67 lbs; 30.4 kg -
 
Note: Amazon links in the table open in the new windows ('Model' column), so feel free to check them for most up-to-date prices and offers.