Groups U1 and U1R Batteries - Dimensions, Features, and Recommendations

BCI Groups U1 and U1R batteries are general-purpose batteries often used in medical and security applications, in wheelchairs, electric scooters, golf carts, lawnmowers, and other garden tools, camping, etc.

BCI group U1 and U1R batteries are mostly AGM and Gel-Cell batteries, with wet/flooded batteries being phased out. Also, lithium-ion U1 batteries are appearing on the market, offering higher capacity, a larger number of charging/discharging cycles, and lower weight, but they also cost more, at least initially.

Updated: September 18, 2023.

Groups U1 and U1R Batteries Features and Specifications

Groups U1 and U1R batteries' physical dimensions are (L x W x H) 7 3/4 x 5 3/16 x 7 5/16 inches (~197 x 132 x 186 mm) with the U1 battery having a positive terminal on the left side, and U1R having a positive terminal post on the right side of the battery (hence the 'R' as part of the label).

Note: terminal posts vary too, so when ordering, be sure to order the battery with proper orientation and with proper terminal posts (for example, F7, F3, B2, etc.).

The following chart lists the most popular BCI Group U1 and U1R batteries and their most important features and specifications:

As one can see, most U1/U1R batteries are intended for general-purpose use, although some are designed even as starting-only batteries.

Also, some models (for example, VMAXTANKS V35-857) are labeled as deep-cycle batteries by their manufacturers, but they are true high-performance dual-purpose batteries.

Group U1 batteries, on average, feature ~35 Ah 20h capacity; they are mostly Sealed Lead-Acid (SLA) Absorbent Glass Mat (AGM) non-spillable, vibration-resistant, maintenance-free batteries that can be mounted in almost any position - mostly in any, except upside down.

High-performance/starting lead-acid U1 batteries feature 300-320 CCA Amps (with some models claiming up to 400+ CCA), while general-purpose U1 batteries are able to provide at least 300-350 Amps for 5-10 seconds - these batteries are commonly used as starting batteries in lawn mowers, garden tractors, power generators, snow blowers, and other similar applications.

Manufacturers rarely state actual Reserve Capacity (RC - number of minutes that a new, fully charged battery can provide 25 Amps at 77°F/25°C while keeping the voltage above 10.5 volts) value, but they often provide constant power and constant current discharging tables, helping the users predict discharge characteristics for different applications.

On average, a good U1 battery is able to provide 19-20 Amps for ~60 minutes. However, a very popular high-performance VMAXTANKS V35-857 battery is able to provide 25 Amps for 75 minutes - which is significantly above the average.

SLA U1 batteries, on average, weigh 23-26 pounds (~10.4 - 11.8 kg) and, thanks to the often built-in carrying handle, can be easily carried around by an adult person.

Lithium-ion U1 batteries are not as common as AGM/Gel-Cell U1 batteries, but they offer huge weight savings, increased number of charging/discharging cycles, larger capacity, lower self-discharge rate, and similar.

For example, VMAXTANKS VPG12C-50Li is a lithium-ion U1 battery with built-in protective electronics (Battery Management System - BMS) that protects the battery from overcharge, over-discharge, short-circuit, and similar undesirable conditions.

Also, it features a nominal capacity of 50 Ah (vs. ~35 Ah AGM 20h capacity), weighs just 12 pounds (~5.4 kg), and can be discharged with 50 Amps continuously with almost no drop in capacity.

Additional features of VMAXTANKS VPG12C-50Li include a battery On/Off switch, LCD display, and USB charging ports (5V/1A, 5V/2.1A), allowing the unit to act as a small power station.

But, VMAXTANKS VPG12C-50Li should not be used for starting/cranking applications - it is able to provide 150 Amps for 3 seconds or 100 Amps for 5 seconds, but no more. Also, VMAXTANKS VPG12C-50Li operates at a slightly higher voltage (up to 16.8 volts) and should be charged with smart battery charters intended for lithium batteries (or at least with lithium-ion battery charging mode).

VMAXTANKS VPG12C-50Li is commonly offered with a smart battery charger that can charge these types of batteries safely, prolonging both runtime and operating life.

Note: every lithium-ion battery has different features of their built-in BMS (Battery Management Systems) and they should be used as recommended by their manufacturer. For example, VMAXTANKS VPG12C-50Li should NOT be connected in series for obtaining higher voltages (24V, 36V, etc.), but can be connected in parallel for obtaining higher capacities.

In the end, all these features dictate the price of the battery.

Note: some models are also offered in pairs or in groups of four.

As starting batteries for smaller internal combustion engines, Weize LFP1235, Power-Sonic PS-12350, and Mighty Max ML35-12 batteries are able to provide 330-350 Amps for at least 5 seconds, which is usually more than long enough for such engines.

Note: if the engine doesn't start after a few short attempts, let the battery 'rest' for a minute or two.

As deep discharge batteries, ExpertPower EXP12330 and Weize LFP1235 are able to provide at least 20 Amps for 60 minutes without the voltage dropping below 10.5 volts.

Note: VMAXTANKS V35-857 is a clear deep discharge winner when compared with other U1 batteries (25 Amps, 75 minutes, down to 10.5 volts), but it also features a 300 CCA value (300 Amps for 30 seconds, with the voltage NOT dropping below 7.2V, at 0°F (-18°C)).

On the other hand, Power-Sonic PS-12350 is able to provide 25 Amps for 60 minutes, but with the voltage drop down to 9 volts (1.5 volts per cell) - such deep discharge can significantly decrease the number of charging/discharging cycles and should be avoided.

Group U1 Batteries in 24 Volts Systems

Group U1 batteries are commonly used in 24-volt systems - two batteries are connected in series, doubling the voltage.

When connecting AGM/Gel-Cell batteries in series, be sure to get the very same batteries - the same battery model, from the same brand, preferably from the same batch.

Many established brands offer their U1 batteries in pairs for 24V systems or as a bundle of 3 batteries for 36V systems.

For example, when two U1 batteries are used to power a wheelchair with 2x250 watts motors at 24 volts, one may expect a maximum current load of 20.8 Amps (~21 Amps) @24V. Several U1 AGM batteries are able to provide such a current for at least 60 minutes.

Since wheelchairs are not used at full power, actual operating time can be several times longer.

Group U1 Batteries as Kayak Trolling Motor Batteries

Group U1 batteries are often used for powering small 12V trolling motors used on kayaks, pontoons, and other smaller crafts.

Kayak trolling motors feature a maximum current of 20-30 Amps, with 25 Amps being their "average maximum" current.

U1 batteries are able to provide 25 Amps for slightly less than 60 minutes - around 45 minutes, having a few more minutes as a safety margin.

But, lithium VMAXTANKS VPG12C-50Li, Nermak 1250, and ExpertPower EP1250, while weighing half the average AGM battery, can provide 25 Amps for almost two hours (at least double the time of the average AGM U1 battery).

Weize TPLI-1236 doesn't feature 50Ah capacity, but it is also able to provide 25 Amps for 1h and 20+ minutes while weighing ~9 pounds.

VMAXTANKS V35-857 is not the cheapest AGM U1 battery on the market, but it is well-liked by people who appreciate its starting features (300 CCA) and its 75-minute RC value.

ExpertPower EXP12350 is able to crank smaller internal combustion engines, but it is often used as a cheaper deep-cycle alternative to VMAXTANKS V35-857.

Weize LFP1235 is a very balanced design and is one of the most popular AGM batteries in this class.

How To Charge U1/U1R Batteries

When the U1/U1R batteries are connected to the electric system of the vehicle/device/application that features a battery charger, let that charger keep the battery charged.

However, when the battery is charged on the bench, it should be charged using advanced battery chargers that monitor the batteries and recharge them as required.

Lead-Acid Batteries

Lead-acid AGM, Gel, Flooded/Wet, Calcium, etc. batteries should be recharged using advanced AGM battery chargers that analyze the battery first and only then charge the battery according to its condition.

Since U1/U1R lead-acid batteries are heavy-duty batteries that are often discharged below 80% DoD, a battery charger should feature desulfation mode and deep discharge recovery/repair mode.

Some manufacturers claim that their lead-acid U1/U1R batteries can be recharged with a current of 10+ Amps, but in order to avoid any additional stress, one should opt for a good ~5 Amps AGM charger.

And when the charging is done, the battery charger should switch to maintenance mode automatically and keep the battery fully charged over longer periods of time.

One such battery charger is the NOCO Genius 6V/12V 5A Smart Battery Charger (Amazon link opens in the new window), which can be used to charge both lead-acid and lithium batteries.

Also, it can recover deeply discharged lead-acid batteries.

When charging lithium U1/U1R batteries, 5A lithium battery chargers are good enough but note that lithium batteries can be recharged using much stronger battery chargers, up to 20-30 Amps.

Again, to avoid any additional stress, go for a good dedicated lithium battery charger or an advanced AGM battery charger that also features lithium battery mode, for example, the NOCO Genius 6V/12V 10A Smart Battery Charger (Amazon link opens in the new window).

U1/U1R Batteries Frequently Asked Questions (FAQ)

Here are some of the most common Frequently Asked Questions (FAQ) about U1/U1R batteries.

What does U1 mean on a battery?

U1 battery means that the battery belongs to the U1 battery group.

Are all U1 batteries the same?

No, U1 batteries differ slightly in size, although all U1/U1R batteries should be able to fit in the standard U1 battery compartment.

Also, these batteries differ in their actual chemistry, discharge features, battery terminal types, etc.

What is the size U1 deep-cycle battery?

U1 batteries feature physical dimensions of (L x W x H) 7 3/4 x 5 3/16 x 7 5/16 inches (~197 x 132 x 186 mm).

What is the difference between U1 and U1R lawn mower batteries?

The main difference between U1 and U1R batteries is in their battery terminal orientation: U1 battery has a positive terminal on the left side, and U1R has a positive terminal post on the right side of the battery (hence the 'R' as part of the label)

What is the highest CCA in a U1 battery?

The average CCA of U1/U1R batteries is around 300-320 Amps, although some models are claiming 400+ CCA Amps.

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Long Story Short: Group U1/U1R batteries are mostly general-purpose batteries, intended for backup, automotive, solar, marine, and other applications. However, some lead-acid U1/U1R batteries are designed as true starting AGM batteries and should be used as such.

Lithium U1/U1R batteries offer large capacity from ultra-light design, but their built-in Battery Management Systems (BMS) are designed to protect the batteries, hence limiting their charging and discharging currents.

When choosing the right model, be sure to pick the battery (or batteries) according to your own needs and requirements.